critical analysis vs literature review

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Difference between a Literature Review and a Critical Review

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• 08 October, 2021

As you read research papers, you may notice that there are two very different kinds of review of prior studies. Sometimes, this section of a paper is called a literature review, and at other times, it is referred to as a critical review or a critical context . These differences may be more commonly seen across different fields. Although both these sections are about reviewing prior and existing studies, this article aims to clarify the differences between the two.

Literature review

A literature review is a summary of prior or existing studies that are related to your own research paper . A literature review can be a part of a research paper or can form a paper in itself . For the former, the literature review is designed as a basis upon which your own current study is designed and built. The latter forms a synthesis of prior studies and is a way to highlight future research agendas or a framework.

Writing a literature review

In a literature review, you should attempt to discuss the arguments and findings in prior studies and then work to build on these studies as you develop your own research. You can also highlight the connection between existing and prior literature to demonstrate how the current study you are presenting can advance your knowledge in the field .

When performing a literature review, you should aim to summarise your discussions using a specific aspect of the literature, such as by topic, time, methodology/ design and findings . By doing so, you should be able to establish an effective way to present the relevant literature and demonstrate the connection between prior studies and your research.

Do note that a literature review does not include a presentation or discussion of any results or findings – this should come at a later point in the paper or study. You should also not impose your subjective viewpoints or opinions on the literature you discuss. 

Critical review

A critical review is also a popular way of reviewing prior and existing studies. It can cover and discuss the main ideas or arguments in a book or an article, or it can review a specific concept, theme, theoretical perspective or key construct found in the existing literature .

However, the key feature that distinguishes a critical review from a literature review is that the former is more than just a summary of different topics or methodologies. It offers more of a reflection and critique of the concept in question, and is engaged by authors to more clearly contextualise their own research within the existing literature and to present their opinions, perspectives and approaches .

Given that a critical review is not just a summary of prior literature, it is generally not considered acceptable to follow the same strategy as for a literature review. Instead, aim to organise and structure your critical review in a way that would enable you to discuss the key concepts, assert your perspectives and locate your arguments and research within the existing body of work. 

Structuring a critical review

A critical review would generally begin with an introduction to the concepts you would like to discuss. Depending on how broad the topics are, this can simply be a brief overview or it could set up a more complex framework. The discussion that follows through the rest of the review will then address and discuss your chosen themes or topics in more depth. 

Writing a critical review

The discussion within a critical review will not only present and summarise themes but also critically engage with the varying arguments, writings and perspectives within those themes. One important thing to note is that, similar to a literature review , you should keep your personal opinions, likes and dislikes out of a review. Whether you personally agree with a study or argument – and whether you like it or not – is immaterial. Instead, you should focus upon the effectiveness and relevance of the arguments , considering such elements as the evidence provided, the interpretations and analysis of the data, whether or not a study may be biased in any way, what further questions or problems it raises or what outstanding gaps and issues need to be addressed.

In conclusion

Although a review of previous and existing literature can be performed and presented in different ways, in essence, any literature or critical review requires a solid understanding of the most prominent work in the field as it relates to your own study. Such an understanding is crucial and significant for you to build upon and synthesise the existing knowledge, and to create and contribute new knowledge to advance the field .

Read previous (fourth) in series: How to refer to other studies or literature in the different sections of a research paper

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Reproduced from Grant, M. J. and Booth, A. (2009), A typology of reviews: an analysis of 14 review types and associated methodologies. Health Information & Libraries Journal, 26: 91–108. doi:10.1111/j.1471-1842.2009.00848.x

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Home » Critical Analysis – Types, Examples and Writing Guide

Critical Analysis – Types, Examples and Writing Guide

Table of Contents

Critical Analysis

Definition:

Critical analysis is a process of examining a piece of work or an idea in a systematic, objective, and analytical way. It involves breaking down complex ideas, concepts, or arguments into smaller, more manageable parts to understand them better.

Types of Critical Analysis

Types of Critical Analysis are as follows:

Literary Analysis

This type of analysis focuses on analyzing and interpreting works of literature , such as novels, poetry, plays, etc. The analysis involves examining the literary devices used in the work, such as symbolism, imagery, and metaphor, and how they contribute to the overall meaning of the work.

Film Analysis

This type of analysis involves examining and interpreting films, including their themes, cinematography, editing, and sound. Film analysis can also include evaluating the director’s style and how it contributes to the overall message of the film.

Art Analysis

This type of analysis involves examining and interpreting works of art , such as paintings, sculptures, and installations. The analysis involves examining the elements of the artwork, such as color, composition, and technique, and how they contribute to the overall meaning of the work.

Cultural Analysis

This type of analysis involves examining and interpreting cultural artifacts , such as advertisements, popular music, and social media posts. The analysis involves examining the cultural context of the artifact and how it reflects and shapes cultural values, beliefs, and norms.

Historical Analysis

This type of analysis involves examining and interpreting historical documents , such as diaries, letters, and government records. The analysis involves examining the historical context of the document and how it reflects the social, political, and cultural attitudes of the time.

Philosophical Analysis

This type of analysis involves examining and interpreting philosophical texts and ideas, such as the works of philosophers and their arguments. The analysis involves evaluating the logical consistency of the arguments and assessing the validity and soundness of the conclusions.

Scientific Analysis

This type of analysis involves examining and interpreting scientific research studies and their findings. The analysis involves evaluating the methods used in the study, the data collected, and the conclusions drawn, and assessing their reliability and validity.

Critical Discourse Analysis

This type of analysis involves examining and interpreting language use in social and political contexts. The analysis involves evaluating the power dynamics and social relationships conveyed through language use and how they shape discourse and social reality.

Comparative Analysis

This type of analysis involves examining and interpreting multiple texts or works of art and comparing them to each other. The analysis involves evaluating the similarities and differences between the texts and how they contribute to understanding the themes and meanings conveyed.

Critical Analysis Format

Critical Analysis Format is as follows:

I. Introduction

• Provide a brief overview of the text, object, or event being analyzed
• Explain the purpose of the analysis and its significance
• Provide background information on the context and relevant historical or cultural factors

II. Description

• Provide a detailed description of the text, object, or event being analyzed
• Identify key themes, ideas, and arguments presented
• Describe the author or creator’s style, tone, and use of language or visual elements

III. Analysis

• Analyze the text, object, or event using critical thinking skills
• Identify the main strengths and weaknesses of the argument or presentation
• Evaluate the reliability and validity of the evidence presented
• Assess any assumptions or biases that may be present in the text, object, or event
• Consider the implications of the argument or presentation for different audiences and contexts

IV. Evaluation

• Provide an overall evaluation of the text, object, or event based on the analysis
• Assess the effectiveness of the argument or presentation in achieving its intended purpose
• Identify any limitations or gaps in the argument or presentation
• Consider any alternative viewpoints or interpretations that could be presented
• Summarize the main points of the analysis and evaluation
• Reiterate the significance of the text, object, or event and its relevance to broader issues or debates
• Provide any recommendations for further research or future developments in the field.

VI. Example

• Provide an example or two to support your analysis and evaluation
• Use quotes or specific details from the text, object, or event to support your claims
• Analyze the example(s) using critical thinking skills and explain how they relate to your overall argument

VII. Conclusion

• Reiterate your thesis statement and summarize your main points
• Provide a final evaluation of the text, object, or event based on your analysis
• Offer recommendations for future research or further developments in the field
• End with a thought-provoking statement or question that encourages the reader to think more deeply about the topic

How to Write Critical Analysis

Writing a critical analysis involves evaluating and interpreting a text, such as a book, article, or film, and expressing your opinion about its quality and significance. Here are some steps you can follow to write a critical analysis:

• Read and re-read the text: Before you begin writing, make sure you have a good understanding of the text. Read it several times and take notes on the key points, themes, and arguments.
• Identify the author’s purpose and audience: Consider why the author wrote the text and who the intended audience is. This can help you evaluate whether the author achieved their goals and whether the text is effective in reaching its audience.
• Analyze the structure and style: Look at the organization of the text and the author’s writing style. Consider how these elements contribute to the overall meaning of the text.
• Evaluate the content : Analyze the author’s arguments, evidence, and conclusions. Consider whether they are logical, convincing, and supported by the evidence presented in the text.
• Consider the context: Think about the historical, cultural, and social context in which the text was written. This can help you understand the author’s perspective and the significance of the text.
• Develop your thesis statement : Based on your analysis, develop a clear and concise thesis statement that summarizes your overall evaluation of the text.
• Support your thesis: Use evidence from the text to support your thesis statement. This can include direct quotes, paraphrases, and examples from the text.
• Write the introduction, body, and conclusion : Organize your analysis into an introduction that provides context and presents your thesis, a body that presents your evidence and analysis, and a conclusion that summarizes your main points and restates your thesis.
• Revise and edit: After you have written your analysis, revise and edit it to ensure that your writing is clear, concise, and well-organized. Check for spelling and grammar errors, and make sure that your analysis is logically sound and supported by evidence.

When to Write Critical Analysis

You may want to write a critical analysis in the following situations:

• Academic Assignments: If you are a student, you may be assigned to write a critical analysis as a part of your coursework. This could include analyzing a piece of literature, a historical event, or a scientific paper.
• Journalism and Media: As a journalist or media person, you may need to write a critical analysis of current events, political speeches, or media coverage.
• Personal Interest: If you are interested in a particular topic, you may want to write a critical analysis to gain a deeper understanding of it. For example, you may want to analyze the themes and motifs in a novel or film that you enjoyed.
• Professional Development : Professionals such as writers, scholars, and researchers often write critical analyses to gain insights into their field of study or work.

Critical Analysis Example

An Example of Critical Analysis Could be as follow:

Research Topic:

The Impact of Online Learning on Student Performance

Introduction:

The introduction of the research topic is clear and provides an overview of the issue. However, it could benefit from providing more background information on the prevalence of online learning and its potential impact on student performance.

Literature Review:

The literature review is comprehensive and well-structured. It covers a broad range of studies that have examined the relationship between online learning and student performance. However, it could benefit from including more recent studies and providing a more critical analysis of the existing literature.

Research Methods:

The research methods are clearly described and appropriate for the research question. The study uses a quasi-experimental design to compare the performance of students who took an online course with those who took the same course in a traditional classroom setting. However, the study may benefit from using a randomized controlled trial design to reduce potential confounding factors.

The results are presented in a clear and concise manner. The study finds that students who took the online course performed similarly to those who took the traditional course. However, the study only measures performance on one course and may not be generalizable to other courses or contexts.

Discussion :

The discussion section provides a thorough analysis of the study’s findings. The authors acknowledge the limitations of the study and provide suggestions for future research. However, they could benefit from discussing potential mechanisms underlying the relationship between online learning and student performance.

Conclusion :

The conclusion summarizes the main findings of the study and provides some implications for future research and practice. However, it could benefit from providing more specific recommendations for implementing online learning programs in educational settings.

Purpose of Critical Analysis

There are several purposes of critical analysis, including:

• To identify and evaluate arguments : Critical analysis helps to identify the main arguments in a piece of writing or speech and evaluate their strengths and weaknesses. This enables the reader to form their own opinion and make informed decisions.
• To assess evidence : Critical analysis involves examining the evidence presented in a text or speech and evaluating its quality and relevance to the argument. This helps to determine the credibility of the claims being made.
• To recognize biases and assumptions : Critical analysis helps to identify any biases or assumptions that may be present in the argument, and evaluate how these affect the credibility of the argument.
• To develop critical thinking skills: Critical analysis helps to develop the ability to think critically, evaluate information objectively, and make reasoned judgments based on evidence.
• To improve communication skills: Critical analysis involves carefully reading and listening to information, evaluating it, and expressing one’s own opinion in a clear and concise manner. This helps to improve communication skills and the ability to express ideas effectively.

Importance of Critical Analysis

Here are some specific reasons why critical analysis is important:

• Helps to identify biases: Critical analysis helps individuals to recognize their own biases and assumptions, as well as the biases of others. By being aware of biases, individuals can better evaluate the credibility and reliability of information.
• Enhances problem-solving skills : Critical analysis encourages individuals to question assumptions and consider multiple perspectives, which can lead to creative problem-solving and innovation.
• Promotes better decision-making: By carefully evaluating evidence and arguments, critical analysis can help individuals make more informed and effective decisions.
• Facilitates understanding: Critical analysis helps individuals to understand complex issues and ideas by breaking them down into smaller parts and evaluating them separately.
• Fosters intellectual growth : Engaging in critical analysis challenges individuals to think deeply and critically, which can lead to intellectual growth and development.

Advantages of Critical Analysis

Some advantages of critical analysis include:

• Improved decision-making: Critical analysis helps individuals make informed decisions by evaluating all available information and considering various perspectives.
• Enhanced problem-solving skills : Critical analysis requires individuals to identify and analyze the root cause of a problem, which can help develop effective solutions.
• Increased creativity : Critical analysis encourages individuals to think outside the box and consider alternative solutions to problems, which can lead to more creative and innovative ideas.
• Improved communication : Critical analysis helps individuals communicate their ideas and opinions more effectively by providing logical and coherent arguments.
• Reduced bias: Critical analysis requires individuals to evaluate information objectively, which can help reduce personal biases and subjective opinions.
• Better understanding of complex issues : Critical analysis helps individuals to understand complex issues by breaking them down into smaller parts, examining each part and understanding how they fit together.
• Greater self-awareness: Critical analysis helps individuals to recognize their own biases, assumptions, and limitations, which can lead to personal growth and development.

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Researcher, Academic Writer, Web developer

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• How to Write a Literature Review | Guide, Examples, & Templates

How to Write a Literature Review | Guide, Examples, & Templates

Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates, and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.

• Quick Run-through
• Step 1 & 2

When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and its scholarly context
• Develop a theoretical framework and methodology for your research
• Position your work in relation to other researchers and theorists
• Show how your research addresses a gap or contributes to a debate
• Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.

Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.

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See an example

Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .

Make a list of keywords

Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can also use boolean operators to help narrow down your search.

Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models, and methods?
• Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.

You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

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To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.

There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.

Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, you can follow these tips:

• Summarize and synthesize: give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: don’t just paraphrase other researchers — add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically evaluate: mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: use transition words and topic sentences to draw connections, comparisons and contrasts

In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.

When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !

This article has been adapted into lecture slides that you can use to teach your students about writing a literature review.

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If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.

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A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarize yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

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The Guide to Literature Reviews

• What is a Literature Review?
• The Purpose of Literature Reviews
• Guidelines for Writing a Literature Review
• How to Organize a Literature Review?
• Software for Literature Reviews
• Using Artificial Intelligence for Literature Reviews
• How to Conduct a Literature Review?
• Common Mistakes and Pitfalls in a Literature Review
• Methods for Literature Reviews
• What is a Systematic Literature Review?
• What is a Narrative Literature Review?
• What is a Descriptive Literature Review?
• What is a Scoping Literature Review?
• What is a Realist Literature Review?
• What is a Critical Review?

When to do a critical literature review?

What is the difference between a critical review and other literature reviews, how to conduct a critical literature review.

• Meta Analysis vs. Literature Review
• What is an Umbrella Literature Review?
• Differences Between Annotated Bibliographies and Literature Reviews
• Literature Review vs. Theoretical Framework
• How to Write a Literature Review?
• How to Structure a Literature Review?
• How to Make a Cover Page for a Literature Review?
• How to Write an Abstract for a Literature Review?
• How to Write a Literature Review Introduction?
• How to Write the Body of a Literature Review?
• How to Write a Literature Review Conclusion?
• How to Make a Literature Review Bibliography?
• How to Format a Literature Review?
• How Long Should a Literature Review Be?
• Examples of Literature Reviews
• How to Present a Literature Review?
• How to Publish a Literature Review?

What is a Critical Literature Review?

A critical literature review is an in-depth evaluation and synthesis of existing research on a specific topic. It involves summarizing the current state of knowledge and critically assessing the strengths, weaknesses, and research gaps to challenge underlying assumptions. This type of review provides a comprehensive understanding of the topic by integrating findings from multiple studies. It highlights inconsistencies and identifies areas that require further investigation by foregrounding the limiting implications of implicit assumptions in current research.

The primary purpose of a critical literature review is to inform research by helping researchers understand what is already known about a topic and what gaps exist in the current literature. A critical literature review ensures that future research builds on a solid foundation by evaluating the quality of previous studies. It helps to develop theoretical frameworks by synthesizing existing theories and findings, which can lead to the proposal of new theoretical frameworks or the refinement of existing ones.

A critical literature review plays a crucial role in identifying gaps in knowledge, which directs future research efforts toward unexplored or under-researched areas. A literature review helps improve the rigour and quality of future research by evaluating existing studies. This critical approach also facilitates theoretical development by contributing to the refinement and advancement of theories within a particular field. A comprehensive synthesis of the literature enhances understanding of the topic, benefiting both researchers and practitioners. For practitioners, the insights gained from a critical literature review can guide the application of research findings to real-world situations, thereby improving practice and outcomes.

A critical literature review is useful in several situations. Use it when you need to understand underlying assumptions in the current state of knowledge on a topic. This type of review is also helpful when you want to identify gaps in the research. By highlighting what is already known based on dominant trends, you can find areas that need further exploration.

A critical literature review is essential when developing a new theoretical framework. By critically evaluating existing theories, you can refine or challenge them. This process is crucial for advancing knowledge in your field. Use a critical literature review when preparing for a research project that adopts an analytical lens that has not been previously considered in that area. It helps you build a solid foundation for your research. By understanding the existing literature, you can design your study to address the gaps and limitations stemming from implicit assumptions in previous research.

For example, in medical research, a critical literature review on the effectiveness of a new drug for treating hypertension might evaluate various clinical trials, comparing methodologies and findings to identify gaps and inconsistencies. For instance, if most studies show positive results but one highlights significant side effects, the review would analyze why these differences exist. This can shed light on not only the efficacy of the drug but also the impacts of diminishing the importance of potential negative outcomes.

Another example is in educational research, where a critical literature review on the impact of technology in the classroom might examine studies on interactive whiteboards and online learning platforms. The review would critically assess the underlying assumptions in previous research, which could involve, for example, questioning dominant discourses that convey the benefits of technology without considering the accessibility of this technology for diverse sociodemographic groups. This synthesis provides a novel perspective of technology's effect on education in different contexts, opening fruitful avenues for further investigation.

A critical review differs from other literature reviews , such as a systematic literature review , in its depth of analysis and approach. While traditional literature reviews summarize existing knowledge, a critical review goes further by providing a detailed evaluation of each source. In a critical literature review, you assess the underlying assumptions of the research methods , the quality of the findings, and the relevance of the theories presented in each research paper.

In a critical review, you synthesize the information to identify patterns and gaps. This synthesis is more than a simple summary; it involves combining findings from different studies to create a new understanding of the topic. This process requires critical thinking and a comprehensive analysis of the literature. The focus on identifying research gaps is a key aspect of critical reviews, which can be facilitated by identifying underlying assumptions and putting forth a novel interpretation. Clearly explaining the limitations of current research helps open new avenues for further research.

A systematic review , on the other hand, follows a structured methodology to collect and analyze data from multiple studies. It aims to provide a comprehensive overview of the existing literature on a specific research question . While systematic reviews are thorough and methodical, they may not always provide the in-depth critical evaluation found in critical literature reviews. Critical reviews, by contrast, emphasize the critical analysis and synthesis of findings to advance knowledge in the field.

By focusing on the detailed evaluation of existing literature, critical reviews highlight areas where research is lacking and suggest potential research gaps. The main difference lies in the critical approach and depth of analysis that challenges dominant understanding in critical literature reviews compared to the structured and methodical approach of systematic reviews.

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Conducting a critical literature review involves several clear steps that guide you through evaluating and synthesizing existing research. Here’s how you can effectively conduct a critical literature review:

Define your research question : Start by clearly defining the research question or problem you want to address. This question will guide your entire review process. Make sure it is specific and relevant to your field of study. A well-defined research question helps you stay focused and ensures that your review is relevant and comprehensive.

Conduct a comprehensive literature search : Begin your literature search by identifying the relevant literature related to your research question. Use academic databases to find research papers, journal articles, books, and other scholarly sources. The literature search process should be thorough to cover all relevant literature and identify key concepts.

Select relevant literature : Once you have gathered a substantial amount of literature, you need to select the most relevant sources. Apply inclusion and exclusion criteria to ensure that you only include studies that are pertinent to your research question. This step involves critical reading to determine the relevance and quality of each source. Focus on recent studies and seminal works that provide a strong foundation for your review.

Evaluate the literature critically : After selecting the relevant literature, evaluate each source critically. Assess the methodologies used in the studies, the findings, and the underlying assumptions of theoretical frameworks. Identify the strengths and weaknesses of each study. This step is crucial for critical evaluation and helps you understand the current state of knowledge in your field. Pay attention to how each study contributes to your research question. This process involves critical thinking and the ability to identify gaps in the literature.

Synthesize the information : Synthesis involves combining the findings from different studies to create a comprehensive understanding of the topic. Identify patterns, trends, and gaps in the existing literature. This step requires critical thinking and helps you build a solid theoretical framework for your own research. Synthesis is more than just summarizing; it involves integrating and interpreting the information from various sources. By doing this, you can provide a critical analysis that highlights the unexplored aspects in the current state of knowledge and thus put forth novel future research directions.

Identify gaps in the literature : A critical literature review should highlight gaps in the existing research. Identify areas where research is lacking or where there are inconsistencies in the findings. This step is essential for identifying future research directions. By explaining the importance of addressing these gaps, you can suggest areas that need further investigation and contribute to the advancement of knowledge in your field. This helps in identifying research gaps and planning future research efforts.

Develop a theoretical framework : Based on your synthesis and identification of gaps, develop a theoretical framework that can be used in your own or other's research. This framework should be grounded in the existing literature but should also address the gaps you have identified. A strong theoretical framework provides a solid foundation for your research and helps you design a study that is both relevant and impactful. The theoretical framework is a critical approach to contextualizing your research within the existing body of knowledge.

A critical literature review is a valuable method for advancing knowledge in your field. By critically evaluating existing literature, you can identify gaps, develop new theoretical frameworks, and build a solid foundation for your own or others' research. This type of review involves several steps, including defining your research question , searching for relevant literature, evaluating sources, and synthesizing information to present a novel perspective. Use a critical literature review when you need to understand the current state of knowledge, identify gaps, and develop new theories. By doing so, you can contribute to the advancement of knowledge in your field.

This critical literature review approach ensures you are well-prepared to address significant research questions, identify gaps, and propose new theoretical frameworks , ultimately advancing the knowledge and understanding in your field. The process involves diligent research, critical evaluation, and careful synthesis, all of which are foundational elements in creating a robust and impactful literature review. Embracing this process will enhance your research skills and lead to meaningful contributions to your field, fostering innovation and progress.

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Which review is that? A guide to review types

• Which review is that?
• Review Comparison Chart
• Decision Tool

Critical Review

• Integrative Review
• Narrative Review
• State of the Art Review
• Narrative Summary
• Systematic Review
• Meta-analysis
• Comparative Effectiveness Review
• Diagnostic Systematic Review
• Network Meta-analysis
• Prognostic Review
• Psychometric Review
• Review of Economic Evaluations
• Systematic Review of Epidemiology Studies
• Living Systematic Reviews
• Umbrella Review
• Review of Reviews
• Rapid Review
• Rapid Evidence Assessment
• Rapid Realist Review
• Qualitative Evidence Synthesis
• Qualitative Interpretive Meta-synthesis
• Qualitative Meta-synthesis
• Qualitative Research Synthesis
• Framework Synthesis - Best-fit Framework Synthesis
• Meta-aggregation
• Meta-ethnography
• Meta-interpretation
• Meta-narrative Review
• Meta-summary
• Thematic Synthesis
• Mixed Methods Synthesis
• Narrative Synthesis
• Bayesian Meta-analysis
• EPPI-Centre Review
• Critical Interpretive Synthesis
• Realist Synthesis - Realist Review
• Scoping Review
• Mapping Review
• Systematised Review
• Concept Synthesis
• Expert Opinion - Policy Review
• Technology Assessment Review
• Methodological Review
• Systematic Search and Review

"A critical review aims to demonstrate that the writer has extensively researched the literature and critically evaluated its quality. It goes beyond mere description of identified articles and includes a degree of analysis and conceptual innovation" and "an effective critical review presents, analyses and synthesizes material from diverse sources". "There is no formal requirement to present methods of the search, synthesis and analysis explicitly" (Grant & Booth 2009).

Further Reading/Resources  

Cooper, Harris M & Cooper, Harris M. Synthesizing research (2017). Research synthesis and meta-analysis : a step-by-step approach (Fifth edition). SAGE Publications, Los Angeles Catalogue Link  

Renate Kahlke , Mark Lee , Kevin W. Eva; Building Blocks for Critical Reviews in Health Professions Education. J Grad Med Educ 1 April 2023; 15 (2): 186–189. doi: https://doi.org/10.4300/JGME-D-23-00155.1

Paré G, Kitsiou S. Chapter 9 Methods for Literature Reviews. In: Lau F, Kuziemsky C, editors. Handbook of eHealth Evaluation: An Evidence-based Approach [Internet]. Victoria (BC): University of Victoria; 2017 Feb 27.  Full text

Younas, A., & Maddigan, J. (2019). Proposing a policy framework for nursing education for fostering compassion in nursing students: A critical review.  Journal of advanced nursing ,  75 (8), 1621–1636. Full Text Rew, L., Young, C. C., Monge, M., & Bogucka, R. (2021). Review: Puberty blockers for transgender and gender diverse youth-a critical review of the literature.  Child and adolescent mental health ,  26 (1), 3–14. Full Text  

References Grant, M. J., & Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies. Health information & libraries journal , 26 (2), 91-108. Full Text

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What is a Literature Review? How to Write It (with Examples)

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

What is the purpose of literature review , a. habitat loss and species extinction: , b. range shifts and phenological changes: , c. ocean acidification and coral reefs: , d. adaptive strategies and conservation efforts: .

• Choose a Topic and Define the Research Question: 
• Decide on the Scope of Your Review: 
• Select Databases for Searches: 
• Conduct Searches and Keep Track: 
• Review the Literature: 
• Organize and Write Your Literature Review: 
• How to write a literature review faster with Paperpal? 

Frequently asked questions 

What is a literature review .

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

1. Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 

2. Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field.

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3. Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 

4. Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 

5. Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 

6. Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example 

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:  

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

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How to write a good literature review 

Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

• Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
• Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
• Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
• Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
• Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

• Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
• Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
• Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
• Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
• Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 

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Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

• Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
• Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
• Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
• Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
• Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

Conducting a literature review 

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:  

• Select a topic that is relevant to your field of study. 
• Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:  

• Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
• Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
• Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:  

• Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
• Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:  

• Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
• Record and document your search strategy for transparency and replicability. 
• Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:  

• Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
• Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
• Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
• Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
• Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:  

• Literature review outline should be based on themes, chronological order, or methodological approaches. 
• Write a clear and coherent narrative that synthesizes the information gathered. 
• Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
• Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

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How to write a literature review faster with Paperpal?  

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The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a good literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. By combining effortless research with an easy citation process, Paperpal Research streamlines the literature review process and empowers you to write faster and with more confidence. Try Paperpal Research now and see for yourself.  

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

References 

• Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
• Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
• Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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Library Guides

Literature reviews: criticality.

• Criticality

Express Critical Analysis

The literature review of a dissertation should include critical analysis. You cannot simply juxtapose the literature you find: you have to  evaluate and draw conclusions from it.  

Paragraph level  

Try expressing your voice in each paragraph of your literature review. Write strong paragraphs. In strong paragraphs your voice can be heard in the topic sentence, development (where you analyse and compare/contrast the sources, sometimes as individual pieces, sometimes in a synthesis) and, even more easily, in the concluding sentence, where you present the "therefore" of the paragraph. 

How to express criticality at the paragraph level:  

Identify the significance of the sources, and why the points they are making are relevant  

Make connections between the sources 

Compare and contrast sources, literatures  

Accept/adopt points made by the sources, with reasons  

Reject the points made by the sources, with reasons (e.g., limitations in the methodology; out of date; limited scope; geographical delimitation) 

Indicate the position you are taking in your own work on the theories and concepts presented by the sources 

Show how limitations in the existing literature create a research gap for you 

Organise the materials, synthesising them in an original way, that sheds new light on the topic.  

To find out more about paragraph writing, check out the Assignment Writing Guides.

Literature review level 

Try to take ownership of the literature review. Remember the purposes of the review (providing background on the subject you are researching and identifying a gap in the existing literature on this subject). Thus, throughout the review:   

Identify the key themes relevant to your subject matter  

Identify the most logical and effective order for your themes 

Relate the sources back to the dissertation's research question 

Shed new light on the topic 

Draw conclusions on the existing literature  

Identify gaps in the literature  

Your literature review should present an argument (which you can recap in the concluding paragraph of the literature review). For instance, 

"The literature says/illustrates/reveals that... there are debates in the literature as of... it can be understood from the literature that... however, there are gaps in the literature... the literature does not specifically address (specific sector/location/population)... there is a lack of independent/recent studies on...  therefore in order to answer the research question(s) (you can repeat the question) this dissertation uses method xyz, as illustrated in the next section (if applicable)". 

Manchester University’s  academic phrase bank  is a great resource for learning new words and phrases. 

Extra Resources

For extra help with all aspects of study skills including how to undertake literature reviews, appointments are available with learning advisors on Engage. 

Appointments are also available with an Academic Engagement Librarian to discuss any issues you might be having with research.

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• Literature Reviews

Literature Reviews: Overview

What is a literature review.

A literature review synthesizes scholarly literature on a topic by evaluating a selection of sources.

It describes common themes, but must also demonstrate the author's understanding of the literature through critical analysis, as well as identify gaps and/or controversies in the research.

The Basics of a Literature Review. (2014). Teaching and Learning Center University of Washington Tacoma. Retrieved from  https://www.tacoma.uw.edu/sites/default/files/2021-05/basics-of-lit-review1.pdf

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Have more questions about your literature review?

• Contact a Librarian for help locating research
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What is the Purpose of a Literature Review?

To help define the focus of your research topic.

To identify research already conducted in your field of interest, find gaps in existing scholarship, and avoid repetition of previous research.

To become familiar with significant earlier research and with current progress and/or controversy in your field of interest.

To  diagnose  the strengths and weaknesses in the works pertaining to your field of interest.

To assess the experts, theoretical approaches, methodologies, results, conclusions, and possible opportunities for future research in your field of interest.

Literature Review vs. Annotated Bibliography

Literature reviews and annotated bibliographies are highly useful for constructing your research project. Both provide an examination of relevant scholarly work pertaining to a specific topic, but there are also significant differences between them.

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Literature Reviews

• What is a Literature Review?
• Steps for Creating a Literature Review
• Providing Evidence / Critical Analysis
• Challenges when writing a Literature Review
• Systematic Literature Reviews

Developing a Literature Review

1. Purpose and Scope

To help you develop a literature review, gather information on existing research, sub-topics, relevant research, and overlaps. Note initial thoughts on the topic - a mind map or list might be helpful - and avoid unfocused reading, collecting irrelevant content.  A literature review serves to place your research within the context of existing knowledge. It demonstrates your understanding of the field and identifies gaps that your research aims to fill. This helps in justifying the relevance and necessity of your study.

To avoid over-reading, set a target word count for each section and limit reading time. Plan backwards from the deadline and move on to other parts of the investigation. Read major texts and explore up-to-date research. Check reference lists and citation indexes for common standard texts. Be guided by research questions and refocus on your topic when needed. Stop reading if you find similar viewpoints or if you're going off topic.

You can use a "Synthesis Matrix" to keep track of your reading notes. This concept map helps you to provide a summary of the literature and its connections is produced as a result of this study. Utilizing referencing software like RefWorks to obtain citations, you can construct the framework for composing your literature evaluation.

2. Source Selection

Focus on searching for academically authoritative texts such as academic books, journals, research reports, and government publications. These sources are critical for ensuring the credibility and reliability of your review. 

• Academic Books: Provide comprehensive coverage of a topic.
• Journal Articles: Offer the most up-to-date research and are essential for a literature review.
• Research Reports: Detailed accounts of specific research projects.
• Government Publications: Official documents that provide reliable data and insights.

3. Thematic Analysis

Instead of merely summarizing sources, identify and discuss key themes that emerge from the literature. This involves interpreting and evaluating how different authors have tackled similar issues and how their findings relate to your research.

4. Critical Evaluation

Adopt a critical attitude towards the sources you review. Scrutinize, question, and dissect the material to ensure that your review is not just descriptive but analytical. This helps in highlighting the significance of various sources and their relevance to your research.

Each work's critical assessment should take into account:

Provenance:  What qualifications does the author have? Are the author's claims backed up by proof, such as first-hand accounts from history, case studies, stories, statistics, and current scientific discoveries? Methodology:  Were the strategies employed to locate, collect, and evaluate the data suitable for tackling the study question? Was the sample size suitable? Were the findings properly reported and interpreted? Objectivity : Is the author's viewpoint impartial or biased? Does the author's thesis get supported by evidence that refutes it, or does it ignore certain important facts? Persuasiveness:  Which of the author's arguments is the strongest or weakest in terms of persuasiveness? Value:  Are the author's claims and deductions believable? Does the study ultimately advance our understanding of the issue in any meaningful way?

5. Categorization

Organize your literature review by grouping sources into categories based on themes, relevance to research questions, theoretical paradigms, or chronology. This helps in presenting your findings in a structured manner.

6. Source Validity

Ensure that the sources you include are valid and reliable. Classic texts may retain their authority over time, but for fields that evolve rapidly, prioritize the most recent research. Always check the credibility of the authors and the impact of their work in the field.

7. Synthesis and Findings

Synthesize the information from various sources to draw conclusions about the current state of knowledge. Identify trends, controversies, and gaps in the literature. Relate your findings to your research questions and suggest future directions for research.

Practical Tips

• Use a variety of sources, including online databases, university libraries, and reference lists from relevant articles. This ensures a comprehensive coverage of the literature.
• Avoid listing sources without analysis. Use tables, bulk citations, and footnotes to manage references efficiently and make your review more readable.
• Writing a literature review is an ongoing process. Start writing early and revise as you read more. This iterative process helps in refining your arguments and identifying additional sources as needed.  

Brown University Library (2024) Organizing and Creating Information. Available at: https://libguides.brown.edu/organize/litreview (Accessed: 30 July 2024).

Pacheco-Vega, R. (2016) Synthesizing different bodies of work in your literature review: The Conceptual Synthesis Excel Dump (CSED) technique . Available at: http://www.raulpacheco.org/2016/06/synthesizing-different-bodies-of-work-in-your-literature-review-the-conceptual-synthesis-excel-dump-technique/ (Accessed: 30 July 2024).

Study Advice at the University of Reading (2024) Literature reviews . Available at: https://libguides.reading.ac.uk/literaturereview/developing (Accessed: 31 July 2024).

Further Reading

Frameworks for creating answerable (re)search questions  How to Guide

Literature Searching How to Guide

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• URL: https://library.lsbu.ac.uk/literaturereviews

Literature Reviews, Critiquing, & Synthesizing Literature

• Literature Review

Types of Literature Reviews

Literature review types -- comparing, learning about study designs, critically appraised topics -- writing, integrative lit review.

• Literature Review Steps Videos
• Critiquing Literature / Critical Review
• Synthesizing Literature
• Summarizing Articles
• Other Lit Review LibGuides

Types of Literature Reviews:

Critically Appraised Topic (CATs) :  A critically appraised topic (or CAT) is a short summary of evidence on a topic of interest, usually focused around a clinical question. A CAT is like a shorter and less rigorous version of a systematic review, summarizing the best available research evidence on a topic.

Integrative Review: A review via a systematic approach that uses a detailed search strategy to find relevant evidence to answer a targeted clinical question. Evidence can come from RCTs, observational studies, qualitative research, clinical experts, and other types of evidence. Does not use summary statistics.

Meta-analysis:  a quantitative statistical analysis of several separate but similar experiments or studies in order to test the pooled data for statistical significance.

Narrative or Traditional Review:  Critical research summary on a topic of interest, often to put a research problem into context. Captures a “snapshot” of the clinical problem or issue.

Rapid Review :  A rapid literature review (RLR) is an alternative to systematic literature review (SLR) that can speed up the analysis of newly published data.

Scoping Review  A s coping review is a descriptive approach, designed to chart the literature around a particular topic. It involves an extensive literature search and often uses structured mapping or charting of the literature.

Systematic Review : Comprehensive search strategies and rigorous research appraisal methods surrounding a clinical issue or question. Evidence is primarily based upon  RCTs . Used to summarize, appraise, & communicate contradictory results or unmanageable amounts of research.

Umbrella Review : An umbrella review is a systematic collection and assessment of multiple systematic reviews and meta-analyses on a specific research topic

• Lit Review vs Systematic Rev vs Meta Analysis
• A typology of reviews: an analysis of 14 review types and associated methodologies. Grant, M. J., & Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies. Health information and libraries journal, 26(2), 91–108. https://doi.org/10.1111/j.1471-1842.2009.00848.x
• Chart comparing Systematic Review Vs Literature Review Chart explaining differences. Chart by L. Kysh, MLIS from U. Ca
• Conducting umbrella reviews Belbasis, L., Bellou, V., & Ioannidis, J. P. (2022). Conducting umbrella reviews. BMJ medicine, 1(1).
• Meeting the review family: exploring review types and associated information retrieval requirements. Sutton, A., Clowes, M., Preston, L., & Booth, A. (2019). Meeting the review family: exploring review types and associated information retrieval requirements. Health Information & Libraries Journal, 36(3), 202-222.
• Part 1: Difference between systematic reviews and rapid reviews (4:43) Cochrane Training video.
• Rapid literature review: definition and methodology Smela, B., Toumi, M., Świerk, K., Francois, C., Biernikiewicz, M., Clay, E., & Boyer, L. (2023). Rapid literature review: definition and methodology. Journal of market access & health policy, 11(1), 2241234. https://doi.org/10.1080/20016689.2023.2241234
• Reviewing Research: Literature Reviews, Scoping Reviews, Systematic Reviews: Differentiating the Three Review Types University of Buffalo LibGuide
• Scoping reviews, systematic reviews, and meta-analysis: Applications in veterinary medicine Sargeant, J. M., & O'Connor, A. M. (2020). Scoping reviews, systematic reviews, and meta-analysis: Applications in veterinary medicine. Frontiers in Veterinary Science, 7, 11-11. https://doi.org/10.3389/fvets.2020.00011
• Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach Munn, Z., Peters, M.D.J., Stern, C. et al. Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. BMC Med Res Methodol 18, 143 (2018). https://doi.org/10.1186/s12874-018-0611-x
• Systematic Review Service: What Type of Review is Right for You? University of Maryland Health Sciences and Human Services Library Decide with type of review. Decision Tree included.
• Systematic vs. Scoping vs. Integrative References Getting Help Systematic vs. Scoping vs. Integrative Review Duquesne University
• What Type of Review is Right for You? Cornell University Library Flowchart to decide about which review to use.
• Combining abbreviated literature searches with single-reviewer screening: Three case studies of rapid reviews. Affengruber, L., Wagner, G., Waffenschmidt, S., Lhachimi, S. K., Nussbaumer-Streit, B., Thaler, K., Griebler, U., Klerings, I., & Gartlehner, G. (2020). Combining abbreviated literature searches with single-reviewer screening: Three case studies of rapid reviews. Systematic Reviews, 9(1), 162-162. https://doi.org/10.1186/s13643-020-01413-7
• Study Design 101 Tutorial by George Washington University. Describes different study designs.

Critically Appraised Topics (CATs)

• CEBMa Guideline for Critically Appraised Topics in Management and Organizations Barends, E., Rousseau, D. M., & Briner, R. B. (2017). CEBMa guideline for critically appraised topics in management and organizations. Center for Evidence-Based Management. https://cebma. org/wp-content/uploads/CEBMa-CAT-Guidelines. pdf.
• Critical Appraisal Skills Programme (CASP) The Critical Appraisal Skills Programme (CASP) was developed in Oxford in 1993 and has since helped to develop an evidence based approach in health and social care, working with local, national and international partner organisations.
• Evidence Based Medicine IV: how to find an evidence-based answer to a clinical question? Make a critically appraised topic! Beckers, G. M. A., Herbst, K., Kaefer, M., Harper, L., Castagnetti, M., Bagli, D., Kalfa, N., Fossum, M., & ESPU Research Committee. (2019). Evidence based medicine IV: How to find an evidence-based answer to a clinical question? make a critically appraised topic. Journal of Pediatric Urology, 15(4), 409-411. https://doi.org/10.1016/j.jpurol.2019.05.009
• EXAMPLE: The Use of Orthotic Insoles to Prevent Lower Limb Overuse Injuries: A Critically Appraised Topic Kelly JL, Valier AR. The Use of Orthotic Insoles to Prevent Lower Limb Overuse Injuries: A Critically Appraised Topic. J Sport Rehabil. 2018 Nov 1;27(6):591-595. doi: 10.1123/jsr.2016-0142. Epub 2018 Oct 13. PMID: 28952905.
• How to Perform a Critically Appraised Topic: Part 1, Ask, Search, and Apply Aine Marie Kelly and Paul Cronin American Journal of Roentgenology November 2011, Volume 197, Number 5
• How to Perform a Critically Appraised Topic: Part 2, Appraise, Evaluate, Generate, and Recommend Aine Marie Kelly and Paul Cronin American Journal of Roentgenology November 2011, Volume 197, Number 5
• How to write a critically appraised topic (CAT) Sadigh, G., Parker, R., Kelly, A. M., & Cronin, P. (2012). How to write a critically appraised topic (CAT). Academic radiology, 19(7), 872–888. https://doi.org/10.1016/j.acra.2012.02.005
• How to write a Critically Appraised Topic: evidence to underpin routine clinical practice Callander J, Anstey AV, Ingram JR, Limpens J, Flohr C, Spuls PI. How to write a Critically Appraised Topic: evidence to underpin routine clinical practice. Br J Dermatol. 2017 Oct;177(4):1007-1013. doi: 10.1111/bjd.15873. Epub 2017 Oct 1. PMID: 28967117.
• What is a Critically Appraised Topic (CAT) Physiopedia

Integrative Review:  A review via a systematic approach that uses a detailed search strategy to find relevant evidence to answer a targeted clinical question. Evidence can come from RCTs, observational studies, qualitative research, clinical experts, and other types of evidence. Does not use summary statistics.

• Conducting integrative reviews: a guide for novice nursing researchers Dhollande S, Taylor A, Meyer S, Scott M. Conducting integrative reviews: a guide for novice nursing researchers. J Res Nurs. 2021 Aug;26(5):427-438. doi: 10.1177/1744987121997907. Epub 2021 Aug 5. PMID: 35251272; PMCID: PMC8894639.
• The integrative review: Updated methodology. Whittemore, R., & Knafl, K. (2005). The integrative review: Updated methodology. Journal of Advanced Nursing, 52(5), 546-553. https://doi.org/10.1111/j.1365-2648.2005.03621.x
• Strategies for completing a successful integrative review Oermann, M. H., & Knafl, K. A. (2021). Strategies for completing a successful integrative review. Nurse Author & Editor, 31(3-4), 65-68.
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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

• Help and Support
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Literature reviews - research guide

• Critical reading and analysis
• Literature reviews home
• Planning your Review & EBP
• Searching for literature
• Managing your results
• Writing your review
• Systematic literature reviews

Critical reading & analysis

• Critical reading
• Analysing sources

Author analysis

• Journal analysis
• Note taking

A critical reader:​ ​

• Does not believe everything they read​ ​
• Questions what they read​ ​
• Rereads if necessary​ ​
• Understands the influence of style​ ​
• Analyses arguments​ ​
• Discounts arguments that are unsupported or based on faulty reasoning

When reading critically, focus on the purpose of your literature review:

• Think about what you expect from the article or chapter, before reading it
• Skim the abstract, headings, conclusion, and the first sentence of each paragraph
• Focus on the arguments presented rather than facts
• Take notes as you read and start to organise your review around themes and ideas
• Consider using a table, matrix or concept map to identify how the different sources relate to each other
• Note four to six points for each study that summarises the main points and conclusions
• Be as objective as possible

Critical appraisal

Critical appraisal is the process of carefully and syst ematically examining research to judge its credibility, its value and its relevance in a specific context.

The aim of critical appraisal is to understand the strengths, weaknesses, and potential for bias in the research. Validity, applicability, and clinical importance should be considered during critical appraisal to ensure that research evidence is used reliably and efficiently and false conclusions are not drawn.

Why do we need to critically appraise the literature?

Critical appraisal is necessary to:

• Assess benefits and strengths for research against flaws and weaknesses
• Decide whether studies have been undertaken in a way that makes their findings reliable
• Make sense of the result
• Know what these results mean in the context of the clinical decision being made
• Assess the usefulness of  the evidence for clinical decisions

Elements of sources

• Abstract: this is what the author wants the reader to take away from their article - what is the starting point? ​ ​
• Introduction:  provides background and a starting point - how does it guide the reader?​ ​
• Materials and methods:  often overlooked but very important - is the methodology understandable, reproducible, direct and robust?
• What do the tables, figures and legends actually report? ​ ​
• What do you think the data means? Decide before reading the discussion​.
• Discussion:  author draws conclusions – how does this correlate with your conclusions?

Evaluation of sources

Consider the following criteria:

• Is the source up-to-date?​
• Does it consider the latest research on your topic?​
• Is the article relevant to your topic?​
• Is the research methodology comprehensively described?​
• Does the work ultimately contribute in any significant way to an understanding of the subject?
• How reputable is the source?​
• Is the source peer-reviewed?​
• What is the source's impact factor ?
• Is the author from a reputable institution?​
• Have you seen the author cited in other sources?​
• Does the data support the conclusions drawn?​
• Are the author's opinions and conclusions convincing? 
• Are the author's arguments supported by evidence (primary material, case studies, narratives, statistics, recent findings)?​ ​
• Is the article properly referenced?​
• What is the purpose of the article and its intended audience?​
• Can you detect any bias in the content?​
• Is the reporting objective?​
• Is contrary data considered or is certain pertinent information ignored to prove the author's point?
• Which of the author's arguments are most/least convincing?​ ​
• Were the objectives achieved? ​ ​
• Hypotheses tested? ​ ​
• How do these results relate to other studies you have found?​ ​
• Do the authors openly discuss any limitations of their study?​ ​
• What else needs be studied in the future?

Interpretation

• Read critically​ ​
• Note 2-4 bullet points for each study that summarises the main points and conclusions​ ​
• Use matrix to analyse findings, relevance and importance of each text​ ​
• Draw attention to studies that are important, influential or that bring a new understanding or method of studying your area of research
• Literature Analysis Worksheet
• Literature Review Matrix

Databases such as Scopus and Web of Science can be used to:

• Locate the papers of a specific author
• Compare the research output of more than one author

The h -index

The h -index is a metric that allows you to compare the publications or research output of authors. This metric is calculated by determining the number of articles (n) written by an author, in the database, that have received the same number or more (n) citations over time. The h -index is a useful metric for comparing rates of publication, as the value is not skewed by a single highly cited paper, nor by a large number of poorly cited papers.

• The h -index is not a static value – if discussing an author’s h-index, you need to specify the date on which the h -index was calculated.
• The h -index is also calculated by other databases/resources and may vary from the h -index given by Scopus – if discussing an author’s h -index, you need to specify the source of the h-index.

See the example below of how an author's  h -index may appear in Scopus.

To locate papers of an author in  Scopus :

• Go to the default Scopus search screen and select Authors tab.
• Enter the author details and affiliation (university). Only include author surname for a comprehensive search. If the author has a common surname, include the first name's initial only.
• The author’s details and the documents that they have written, and which are indexed by Scopus, will be retrieved. Click on the author’s name to see a full list of their publications.

The information about the author will also tell you:

• How many of their publications have been indexed by Scopus
• How many times their publications have been cited
• Which of their publications are most highly cited
• Who they have co-authored papers with
• Their publication and citation trends for the past nine years
• Their h -index

See the Scopus resources below for more help:

• How to search for authors by topic
• How to assess an author's impact
• How to keep track of an author
• How to create citation overviews in Scopus

Web of Science Core Collection

To locate papers of an author in Web of Science Core Collection (WoS CC):

• Go to the default WoS CC search screen and select Researchers tab.
• Enter the author's surname and first name's initial.

The author’s details and the papers that they have written, and which are indexed by WoS CC, will be retrieved. Click on the Publications tab to see a full list of their publications.

• How many of their publications have been indexed by WoS CC

The author's citation report will tell you:

The Measuring research quality and impact guide has more detailed information on author analytics:

• Measuring research quality and impact

Source/journal analysis

Databases such as Scopus and Web of Science  (including CAB Abstracts ) can be used to determine the quality of journals in a discipline or field of research. For more information on journal analytics, please see the relevant section of our guide on Measuring Research Quality & Impact:

• Journal quality & impact (in Measuring research quality & impact guide)

Taking clear, legible notes will help to focus your critical reading and analysis of your literature review sources. When taking notes, avoid plagiarism by:

•  Keeping track of the difference between information from your sources and from your own ideas
•  Providing clear references, including page numbers

Note taking methods

Some effective methods of note-taking include:

• Outlining method. Use headings, sub-headings and bullet points to organize topics
• Cornell method. Use two columns - in one column write your summary of the authors' conclusions and evidence, and in the other column write down your own analysis and other comments
• Charting method. Create a list of topics or points you want to write about - use a column for each one. As you read, add references and make notes in the appropriate column
• Sentence method. Simply write down new ideas and bits of information as a numbered  sentence
• Mapping method. Write down key concepts and terms, with related ideas radiating out from these

You may consider using the matrix below for your note taking and analysis:

Critical reading & analysis checklist

• Does your literature review highlight flaws, gaps, or shortcomings of specific texts or groups of texts?
• Have you identified areas that have not yet been researched or have not yet been researched sufficiently?
• Does the literature demonstrate a change over time or recent developments that make your research relevant now?
• Are you able to discuss research methods used to study this topic and/or related topics?
• Can you clearly state why your research is necessary?
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Chapter 9 methods for literature reviews.

Guy Paré and Spyros Kitsiou .

9.1. Introduction

Literature reviews play a critical role in scholarship because science remains, first and foremost, a cumulative endeavour ( vom Brocke et al., 2009 ). As in any academic discipline, rigorous knowledge syntheses are becoming indispensable in keeping up with an exponentially growing eHealth literature, assisting practitioners, academics, and graduate students in finding, evaluating, and synthesizing the contents of many empirical and conceptual papers. Among other methods, literature reviews are essential for: (a) identifying what has been written on a subject or topic; (b) determining the extent to which a specific research area reveals any interpretable trends or patterns; (c) aggregating empirical findings related to a narrow research question to support evidence-based practice; (d) generating new frameworks and theories; and (e) identifying topics or questions requiring more investigation ( Paré, Trudel, Jaana, & Kitsiou, 2015 ).

Literature reviews can take two major forms. The most prevalent one is the “literature review” or “background” section within a journal paper or a chapter in a graduate thesis. This section synthesizes the extant literature and usually identifies the gaps in knowledge that the empirical study addresses ( Sylvester, Tate, & Johnstone, 2013 ). It may also provide a theoretical foundation for the proposed study, substantiate the presence of the research problem, justify the research as one that contributes something new to the cumulated knowledge, or validate the methods and approaches for the proposed study ( Hart, 1998 ; Levy & Ellis, 2006 ).

The second form of literature review, which is the focus of this chapter, constitutes an original and valuable work of research in and of itself ( Paré et al., 2015 ). Rather than providing a base for a researcher’s own work, it creates a solid starting point for all members of the community interested in a particular area or topic ( Mulrow, 1987 ). The so-called “review article” is a journal-length paper which has an overarching purpose to synthesize the literature in a field, without collecting or analyzing any primary data ( Green, Johnson, & Adams, 2006 ).

When appropriately conducted, review articles represent powerful information sources for practitioners looking for state-of-the art evidence to guide their decision-making and work practices ( Paré et al., 2015 ). Further, high-quality reviews become frequently cited pieces of work which researchers seek out as a first clear outline of the literature when undertaking empirical studies ( Cooper, 1988 ; Rowe, 2014 ). Scholars who track and gauge the impact of articles have found that review papers are cited and downloaded more often than any other type of published article ( Cronin, Ryan, & Coughlan, 2008 ; Montori, Wilczynski, Morgan, Haynes, & Hedges, 2003 ; Patsopoulos, Analatos, & Ioannidis, 2005 ). The reason for their popularity may be the fact that reading the review enables one to have an overview, if not a detailed knowledge of the area in question, as well as references to the most useful primary sources ( Cronin et al., 2008 ). Although they are not easy to conduct, the commitment to complete a review article provides a tremendous service to one’s academic community ( Paré et al., 2015 ; Petticrew & Roberts, 2006 ). Most, if not all, peer-reviewed journals in the fields of medical informatics publish review articles of some type.

The main objectives of this chapter are fourfold: (a) to provide an overview of the major steps and activities involved in conducting a stand-alone literature review; (b) to describe and contrast the different types of review articles that can contribute to the eHealth knowledge base; (c) to illustrate each review type with one or two examples from the eHealth literature; and (d) to provide a series of recommendations for prospective authors of review articles in this domain.

9.2. Overview of the Literature Review Process and Steps

As explained in Templier and Paré (2015) , there are six generic steps involved in conducting a review article:

• formulating the research question(s) and objective(s),
• searching the extant literature,
• screening for inclusion,
• assessing the quality of primary studies,
• extracting data, and
• analyzing data.

Although these steps are presented here in sequential order, one must keep in mind that the review process can be iterative and that many activities can be initiated during the planning stage and later refined during subsequent phases ( Finfgeld-Connett & Johnson, 2013 ; Kitchenham & Charters, 2007 ).

Formulating the research question(s) and objective(s): As a first step, members of the review team must appropriately justify the need for the review itself ( Petticrew & Roberts, 2006 ), identify the review’s main objective(s) ( Okoli & Schabram, 2010 ), and define the concepts or variables at the heart of their synthesis ( Cooper & Hedges, 2009 ; Webster & Watson, 2002 ). Importantly, they also need to articulate the research question(s) they propose to investigate ( Kitchenham & Charters, 2007 ). In this regard, we concur with Jesson, Matheson, and Lacey (2011) that clearly articulated research questions are key ingredients that guide the entire review methodology; they underscore the type of information that is needed, inform the search for and selection of relevant literature, and guide or orient the subsequent analysis. Searching the extant literature: The next step consists of searching the literature and making decisions about the suitability of material to be considered in the review ( Cooper, 1988 ). There exist three main coverage strategies. First, exhaustive coverage means an effort is made to be as comprehensive as possible in order to ensure that all relevant studies, published and unpublished, are included in the review and, thus, conclusions are based on this all-inclusive knowledge base. The second type of coverage consists of presenting materials that are representative of most other works in a given field or area. Often authors who adopt this strategy will search for relevant articles in a small number of top-tier journals in a field ( Paré et al., 2015 ). In the third strategy, the review team concentrates on prior works that have been central or pivotal to a particular topic. This may include empirical studies or conceptual papers that initiated a line of investigation, changed how problems or questions were framed, introduced new methods or concepts, or engendered important debate ( Cooper, 1988 ). Screening for inclusion: The following step consists of evaluating the applicability of the material identified in the preceding step ( Levy & Ellis, 2006 ; vom Brocke et al., 2009 ). Once a group of potential studies has been identified, members of the review team must screen them to determine their relevance ( Petticrew & Roberts, 2006 ). A set of predetermined rules provides a basis for including or excluding certain studies. This exercise requires a significant investment on the part of researchers, who must ensure enhanced objectivity and avoid biases or mistakes. As discussed later in this chapter, for certain types of reviews there must be at least two independent reviewers involved in the screening process and a procedure to resolve disagreements must also be in place ( Liberati et al., 2009 ; Shea et al., 2009 ). Assessing the quality of primary studies: In addition to screening material for inclusion, members of the review team may need to assess the scientific quality of the selected studies, that is, appraise the rigour of the research design and methods. Such formal assessment, which is usually conducted independently by at least two coders, helps members of the review team refine which studies to include in the final sample, determine whether or not the differences in quality may affect their conclusions, or guide how they analyze the data and interpret the findings ( Petticrew & Roberts, 2006 ). Ascribing quality scores to each primary study or considering through domain-based evaluations which study components have or have not been designed and executed appropriately makes it possible to reflect on the extent to which the selected study addresses possible biases and maximizes validity ( Shea et al., 2009 ). Extracting data: The following step involves gathering or extracting applicable information from each primary study included in the sample and deciding what is relevant to the problem of interest ( Cooper & Hedges, 2009 ). Indeed, the type of data that should be recorded mainly depends on the initial research questions ( Okoli & Schabram, 2010 ). However, important information may also be gathered about how, when, where and by whom the primary study was conducted, the research design and methods, or qualitative/quantitative results ( Cooper & Hedges, 2009 ). Analyzing and synthesizing data : As a final step, members of the review team must collate, summarize, aggregate, organize, and compare the evidence extracted from the included studies. The extracted data must be presented in a meaningful way that suggests a new contribution to the extant literature ( Jesson et al., 2011 ). Webster and Watson (2002) warn researchers that literature reviews should be much more than lists of papers and should provide a coherent lens to make sense of extant knowledge on a given topic. There exist several methods and techniques for synthesizing quantitative (e.g., frequency analysis, meta-analysis) and qualitative (e.g., grounded theory, narrative analysis, meta-ethnography) evidence ( Dixon-Woods, Agarwal, Jones, Young, & Sutton, 2005 ; Thomas & Harden, 2008 ).

9.3. Types of Review Articles and Brief Illustrations

EHealth researchers have at their disposal a number of approaches and methods for making sense out of existing literature, all with the purpose of casting current research findings into historical contexts or explaining contradictions that might exist among a set of primary research studies conducted on a particular topic. Our classification scheme is largely inspired from Paré and colleagues’ (2015) typology. Below we present and illustrate those review types that we feel are central to the growth and development of the eHealth domain.

9.3.1. Narrative Reviews

The narrative review is the “traditional” way of reviewing the extant literature and is skewed towards a qualitative interpretation of prior knowledge ( Sylvester et al., 2013 ). Put simply, a narrative review attempts to summarize or synthesize what has been written on a particular topic but does not seek generalization or cumulative knowledge from what is reviewed ( Davies, 2000 ; Green et al., 2006 ). Instead, the review team often undertakes the task of accumulating and synthesizing the literature to demonstrate the value of a particular point of view ( Baumeister & Leary, 1997 ). As such, reviewers may selectively ignore or limit the attention paid to certain studies in order to make a point. In this rather unsystematic approach, the selection of information from primary articles is subjective, lacks explicit criteria for inclusion and can lead to biased interpretations or inferences ( Green et al., 2006 ). There are several narrative reviews in the particular eHealth domain, as in all fields, which follow such an unstructured approach ( Silva et al., 2015 ; Paul et al., 2015 ).

Despite these criticisms, this type of review can be very useful in gathering together a volume of literature in a specific subject area and synthesizing it. As mentioned above, its primary purpose is to provide the reader with a comprehensive background for understanding current knowledge and highlighting the significance of new research ( Cronin et al., 2008 ). Faculty like to use narrative reviews in the classroom because they are often more up to date than textbooks, provide a single source for students to reference, and expose students to peer-reviewed literature ( Green et al., 2006 ). For researchers, narrative reviews can inspire research ideas by identifying gaps or inconsistencies in a body of knowledge, thus helping researchers to determine research questions or formulate hypotheses. Importantly, narrative reviews can also be used as educational articles to bring practitioners up to date with certain topics of issues ( Green et al., 2006 ).

Recently, there have been several efforts to introduce more rigour in narrative reviews that will elucidate common pitfalls and bring changes into their publication standards. Information systems researchers, among others, have contributed to advancing knowledge on how to structure a “traditional” review. For instance, Levy and Ellis (2006) proposed a generic framework for conducting such reviews. Their model follows the systematic data processing approach comprised of three steps, namely: (a) literature search and screening; (b) data extraction and analysis; and (c) writing the literature review. They provide detailed and very helpful instructions on how to conduct each step of the review process. As another methodological contribution, vom Brocke et al. (2009) offered a series of guidelines for conducting literature reviews, with a particular focus on how to search and extract the relevant body of knowledge. Last, Bandara, Miskon, and Fielt (2011) proposed a structured, predefined and tool-supported method to identify primary studies within a feasible scope, extract relevant content from identified articles, synthesize and analyze the findings, and effectively write and present the results of the literature review. We highly recommend that prospective authors of narrative reviews consult these useful sources before embarking on their work.

Darlow and Wen (2015) provide a good example of a highly structured narrative review in the eHealth field. These authors synthesized published articles that describe the development process of mobile health (m-health) interventions for patients’ cancer care self-management. As in most narrative reviews, the scope of the research questions being investigated is broad: (a) how development of these systems are carried out; (b) which methods are used to investigate these systems; and (c) what conclusions can be drawn as a result of the development of these systems. To provide clear answers to these questions, a literature search was conducted on six electronic databases and Google Scholar . The search was performed using several terms and free text words, combining them in an appropriate manner. Four inclusion and three exclusion criteria were utilized during the screening process. Both authors independently reviewed each of the identified articles to determine eligibility and extract study information. A flow diagram shows the number of studies identified, screened, and included or excluded at each stage of study selection. In terms of contributions, this review provides a series of practical recommendations for m-health intervention development.

9.3.2. Descriptive or Mapping Reviews

The primary goal of a descriptive review is to determine the extent to which a body of knowledge in a particular research topic reveals any interpretable pattern or trend with respect to pre-existing propositions, theories, methodologies or findings ( King & He, 2005 ; Paré et al., 2015 ). In contrast with narrative reviews, descriptive reviews follow a systematic and transparent procedure, including searching, screening and classifying studies ( Petersen, Vakkalanka, & Kuzniarz, 2015 ). Indeed, structured search methods are used to form a representative sample of a larger group of published works ( Paré et al., 2015 ). Further, authors of descriptive reviews extract from each study certain characteristics of interest, such as publication year, research methods, data collection techniques, and direction or strength of research outcomes (e.g., positive, negative, or non-significant) in the form of frequency analysis to produce quantitative results ( Sylvester et al., 2013 ). In essence, each study included in a descriptive review is treated as the unit of analysis and the published literature as a whole provides a database from which the authors attempt to identify any interpretable trends or draw overall conclusions about the merits of existing conceptualizations, propositions, methods or findings ( Paré et al., 2015 ). In doing so, a descriptive review may claim that its findings represent the state of the art in a particular domain ( King & He, 2005 ).

In the fields of health sciences and medical informatics, reviews that focus on examining the range, nature and evolution of a topic area are described by Anderson, Allen, Peckham, and Goodwin (2008) as mapping reviews . Like descriptive reviews, the research questions are generic and usually relate to publication patterns and trends. There is no preconceived plan to systematically review all of the literature although this can be done. Instead, researchers often present studies that are representative of most works published in a particular area and they consider a specific time frame to be mapped.

An example of this approach in the eHealth domain is offered by DeShazo, Lavallie, and Wolf (2009). The purpose of this descriptive or mapping review was to characterize publication trends in the medical informatics literature over a 20-year period (1987 to 2006). To achieve this ambitious objective, the authors performed a bibliometric analysis of medical informatics citations indexed in medline using publication trends, journal frequencies, impact factors, Medical Subject Headings (MeSH) term frequencies, and characteristics of citations. Findings revealed that there were over 77,000 medical informatics articles published during the covered period in numerous journals and that the average annual growth rate was 12%. The MeSH term analysis also suggested a strong interdisciplinary trend. Finally, average impact scores increased over time with two notable growth periods. Overall, patterns in research outputs that seem to characterize the historic trends and current components of the field of medical informatics suggest it may be a maturing discipline (DeShazo et al., 2009).

9.3.3. Scoping Reviews

Scoping reviews attempt to provide an initial indication of the potential size and nature of the extant literature on an emergent topic (Arksey & O’Malley, 2005; Daudt, van Mossel, & Scott, 2013 ; Levac, Colquhoun, & O’Brien, 2010). A scoping review may be conducted to examine the extent, range and nature of research activities in a particular area, determine the value of undertaking a full systematic review (discussed next), or identify research gaps in the extant literature ( Paré et al., 2015 ). In line with their main objective, scoping reviews usually conclude with the presentation of a detailed research agenda for future works along with potential implications for both practice and research.

Unlike narrative and descriptive reviews, the whole point of scoping the field is to be as comprehensive as possible, including grey literature (Arksey & O’Malley, 2005). Inclusion and exclusion criteria must be established to help researchers eliminate studies that are not aligned with the research questions. It is also recommended that at least two independent coders review abstracts yielded from the search strategy and then the full articles for study selection ( Daudt et al., 2013 ). The synthesized evidence from content or thematic analysis is relatively easy to present in tabular form (Arksey & O’Malley, 2005; Thomas & Harden, 2008 ).

One of the most highly cited scoping reviews in the eHealth domain was published by Archer, Fevrier-Thomas, Lokker, McKibbon, and Straus (2011) . These authors reviewed the existing literature on personal health record ( phr ) systems including design, functionality, implementation, applications, outcomes, and benefits. Seven databases were searched from 1985 to March 2010. Several search terms relating to phr s were used during this process. Two authors independently screened titles and abstracts to determine inclusion status. A second screen of full-text articles, again by two independent members of the research team, ensured that the studies described phr s. All in all, 130 articles met the criteria and their data were extracted manually into a database. The authors concluded that although there is a large amount of survey, observational, cohort/panel, and anecdotal evidence of phr benefits and satisfaction for patients, more research is needed to evaluate the results of phr implementations. Their in-depth analysis of the literature signalled that there is little solid evidence from randomized controlled trials or other studies through the use of phr s. Hence, they suggested that more research is needed that addresses the current lack of understanding of optimal functionality and usability of these systems, and how they can play a beneficial role in supporting patient self-management ( Archer et al., 2011 ).

9.3.4. Forms of Aggregative Reviews

Healthcare providers, practitioners, and policy-makers are nowadays overwhelmed with large volumes of information, including research-based evidence from numerous clinical trials and evaluation studies, assessing the effectiveness of health information technologies and interventions ( Ammenwerth & de Keizer, 2004 ; Deshazo et al., 2009 ). It is unrealistic to expect that all these disparate actors will have the time, skills, and necessary resources to identify the available evidence in the area of their expertise and consider it when making decisions. Systematic reviews that involve the rigorous application of scientific strategies aimed at limiting subjectivity and bias (i.e., systematic and random errors) can respond to this challenge.

Systematic reviews attempt to aggregate, appraise, and synthesize in a single source all empirical evidence that meet a set of previously specified eligibility criteria in order to answer a clearly formulated and often narrow research question on a particular topic of interest to support evidence-based practice ( Liberati et al., 2009 ). They adhere closely to explicit scientific principles ( Liberati et al., 2009 ) and rigorous methodological guidelines (Higgins & Green, 2008) aimed at reducing random and systematic errors that can lead to deviations from the truth in results or inferences. The use of explicit methods allows systematic reviews to aggregate a large body of research evidence, assess whether effects or relationships are in the same direction and of the same general magnitude, explain possible inconsistencies between study results, and determine the strength of the overall evidence for every outcome of interest based on the quality of included studies and the general consistency among them ( Cook, Mulrow, & Haynes, 1997 ). The main procedures of a systematic review involve:

• Formulating a review question and developing a search strategy based on explicit inclusion criteria for the identification of eligible studies (usually described in the context of a detailed review protocol).
• Searching for eligible studies using multiple databases and information sources, including grey literature sources, without any language restrictions.
• Selecting studies, extracting data, and assessing risk of bias in a duplicate manner using two independent reviewers to avoid random or systematic errors in the process.
• Analyzing data using quantitative or qualitative methods.
• Presenting results in summary of findings tables.
• Interpreting results and drawing conclusions.

Many systematic reviews, but not all, use statistical methods to combine the results of independent studies into a single quantitative estimate or summary effect size. Known as meta-analyses , these reviews use specific data extraction and statistical techniques (e.g., network, frequentist, or Bayesian meta-analyses) to calculate from each study by outcome of interest an effect size along with a confidence interval that reflects the degree of uncertainty behind the point estimate of effect ( Borenstein, Hedges, Higgins, & Rothstein, 2009 ; Deeks, Higgins, & Altman, 2008 ). Subsequently, they use fixed or random-effects analysis models to combine the results of the included studies, assess statistical heterogeneity, and calculate a weighted average of the effect estimates from the different studies, taking into account their sample sizes. The summary effect size is a value that reflects the average magnitude of the intervention effect for a particular outcome of interest or, more generally, the strength of a relationship between two variables across all studies included in the systematic review. By statistically combining data from multiple studies, meta-analyses can create more precise and reliable estimates of intervention effects than those derived from individual studies alone, when these are examined independently as discrete sources of information.

The review by Gurol-Urganci, de Jongh, Vodopivec-Jamsek, Atun, and Car (2013) on the effects of mobile phone messaging reminders for attendance at healthcare appointments is an illustrative example of a high-quality systematic review with meta-analysis. Missed appointments are a major cause of inefficiency in healthcare delivery with substantial monetary costs to health systems. These authors sought to assess whether mobile phone-based appointment reminders delivered through Short Message Service ( sms ) or Multimedia Messaging Service ( mms ) are effective in improving rates of patient attendance and reducing overall costs. To this end, they conducted a comprehensive search on multiple databases using highly sensitive search strategies without language or publication-type restrictions to identify all rct s that are eligible for inclusion. In order to minimize the risk of omitting eligible studies not captured by the original search, they supplemented all electronic searches with manual screening of trial registers and references contained in the included studies. Study selection, data extraction, and risk of bias assessments were performed inde­­pen­dently by two coders using standardized methods to ensure consistency and to eliminate potential errors. Findings from eight rct s involving 6,615 participants were pooled into meta-analyses to calculate the magnitude of effects that mobile text message reminders have on the rate of attendance at healthcare appointments compared to no reminders and phone call reminders.

Meta-analyses are regarded as powerful tools for deriving meaningful conclusions. However, there are situations in which it is neither reasonable nor appropriate to pool studies together using meta-analytic methods simply because there is extensive clinical heterogeneity between the included studies or variation in measurement tools, comparisons, or outcomes of interest. In these cases, systematic reviews can use qualitative synthesis methods such as vote counting, content analysis, classification schemes and tabulations, as an alternative approach to narratively synthesize the results of the independent studies included in the review. This form of review is known as qualitative systematic review.

A rigorous example of one such review in the eHealth domain is presented by Mickan, Atherton, Roberts, Heneghan, and Tilson (2014) on the use of handheld computers by healthcare professionals and their impact on access to information and clinical decision-making. In line with the methodological guide­lines for systematic reviews, these authors: (a) developed and registered with prospero ( www.crd.york.ac.uk/ prospero / ) an a priori review protocol; (b) conducted comprehensive searches for eligible studies using multiple databases and other supplementary strategies (e.g., forward searches); and (c) subsequently carried out study selection, data extraction, and risk of bias assessments in a duplicate manner to eliminate potential errors in the review process. Heterogeneity between the included studies in terms of reported outcomes and measures precluded the use of meta-analytic methods. To this end, the authors resorted to using narrative analysis and synthesis to describe the effectiveness of handheld computers on accessing information for clinical knowledge, adherence to safety and clinical quality guidelines, and diagnostic decision-making.

In recent years, the number of systematic reviews in the field of health informatics has increased considerably. Systematic reviews with discordant findings can cause great confusion and make it difficult for decision-makers to interpret the review-level evidence ( Moher, 2013 ). Therefore, there is a growing need for appraisal and synthesis of prior systematic reviews to ensure that decision-making is constantly informed by the best available accumulated evidence. Umbrella reviews , also known as overviews of systematic reviews, are tertiary types of evidence synthesis that aim to accomplish this; that is, they aim to compare and contrast findings from multiple systematic reviews and meta-analyses ( Becker & Oxman, 2008 ). Umbrella reviews generally adhere to the same principles and rigorous methodological guidelines used in systematic reviews. However, the unit of analysis in umbrella reviews is the systematic review rather than the primary study ( Becker & Oxman, 2008 ). Unlike systematic reviews that have a narrow focus of inquiry, umbrella reviews focus on broader research topics for which there are several potential interventions ( Smith, Devane, Begley, & Clarke, 2011 ). A recent umbrella review on the effects of home telemonitoring interventions for patients with heart failure critically appraised, compared, and synthesized evidence from 15 systematic reviews to investigate which types of home telemonitoring technologies and forms of interventions are more effective in reducing mortality and hospital admissions ( Kitsiou, Paré, & Jaana, 2015 ).

9.3.5. Realist Reviews

Realist reviews are theory-driven interpretative reviews developed to inform, enhance, or supplement conventional systematic reviews by making sense of heterogeneous evidence about complex interventions applied in diverse contexts in a way that informs policy decision-making ( Greenhalgh, Wong, Westhorp, & Pawson, 2011 ). They originated from criticisms of positivist systematic reviews which centre on their “simplistic” underlying assumptions ( Oates, 2011 ). As explained above, systematic reviews seek to identify causation. Such logic is appropriate for fields like medicine and education where findings of randomized controlled trials can be aggregated to see whether a new treatment or intervention does improve outcomes. However, many argue that it is not possible to establish such direct causal links between interventions and outcomes in fields such as social policy, management, and information systems where for any intervention there is unlikely to be a regular or consistent outcome ( Oates, 2011 ; Pawson, 2006 ; Rousseau, Manning, & Denyer, 2008 ).

To circumvent these limitations, Pawson, Greenhalgh, Harvey, and Walshe (2005) have proposed a new approach for synthesizing knowledge that seeks to unpack the mechanism of how “complex interventions” work in particular contexts. The basic research question — what works? — which is usually associated with systematic reviews changes to: what is it about this intervention that works, for whom, in what circumstances, in what respects and why? Realist reviews have no particular preference for either quantitative or qualitative evidence. As a theory-building approach, a realist review usually starts by articulating likely underlying mechanisms and then scrutinizes available evidence to find out whether and where these mechanisms are applicable ( Shepperd et al., 2009 ). Primary studies found in the extant literature are viewed as case studies which can test and modify the initial theories ( Rousseau et al., 2008 ).

The main objective pursued in the realist review conducted by Otte-Trojel, de Bont, Rundall, and van de Klundert (2014) was to examine how patient portals contribute to health service delivery and patient outcomes. The specific goals were to investigate how outcomes are produced and, most importantly, how variations in outcomes can be explained. The research team started with an exploratory review of background documents and research studies to identify ways in which patient portals may contribute to health service delivery and patient outcomes. The authors identified six main ways which represent “educated guesses” to be tested against the data in the evaluation studies. These studies were identified through a formal and systematic search in four databases between 2003 and 2013. Two members of the research team selected the articles using a pre-established list of inclusion and exclusion criteria and following a two-step procedure. The authors then extracted data from the selected articles and created several tables, one for each outcome category. They organized information to bring forward those mechanisms where patient portals contribute to outcomes and the variation in outcomes across different contexts.

9.3.6. Critical Reviews

Lastly, critical reviews aim to provide a critical evaluation and interpretive analysis of existing literature on a particular topic of interest to reveal strengths, weaknesses, contradictions, controversies, inconsistencies, and/or other important issues with respect to theories, hypotheses, research methods or results ( Baumeister & Leary, 1997 ; Kirkevold, 1997 ). Unlike other review types, critical reviews attempt to take a reflective account of the research that has been done in a particular area of interest, and assess its credibility by using appraisal instruments or critical interpretive methods. In this way, critical reviews attempt to constructively inform other scholars about the weaknesses of prior research and strengthen knowledge development by giving focus and direction to studies for further improvement ( Kirkevold, 1997 ).

Kitsiou, Paré, and Jaana (2013) provide an example of a critical review that assessed the methodological quality of prior systematic reviews of home telemonitoring studies for chronic patients. The authors conducted a comprehensive search on multiple databases to identify eligible reviews and subsequently used a validated instrument to conduct an in-depth quality appraisal. Results indicate that the majority of systematic reviews in this particular area suffer from important methodological flaws and biases that impair their internal validity and limit their usefulness for clinical and decision-making purposes. To this end, they provide a number of recommendations to strengthen knowledge development towards improving the design and execution of future reviews on home telemonitoring.

9.4. Summary

Table 9.1 outlines the main types of literature reviews that were described in the previous sub-sections and summarizes the main characteristics that distinguish one review type from another. It also includes key references to methodological guidelines and useful sources that can be used by eHealth scholars and researchers for planning and developing reviews.

Typology of Literature Reviews (adapted from Paré et al., 2015).

As shown in Table 9.1 , each review type addresses different kinds of research questions or objectives, which subsequently define and dictate the methods and approaches that need to be used to achieve the overarching goal(s) of the review. For example, in the case of narrative reviews, there is greater flexibility in searching and synthesizing articles ( Green et al., 2006 ). Researchers are often relatively free to use a diversity of approaches to search, identify, and select relevant scientific articles, describe their operational characteristics, present how the individual studies fit together, and formulate conclusions. On the other hand, systematic reviews are characterized by their high level of systematicity, rigour, and use of explicit methods, based on an “a priori” review plan that aims to minimize bias in the analysis and synthesis process (Higgins & Green, 2008). Some reviews are exploratory in nature (e.g., scoping/mapping reviews), whereas others may be conducted to discover patterns (e.g., descriptive reviews) or involve a synthesis approach that may include the critical analysis of prior research ( Paré et al., 2015 ). Hence, in order to select the most appropriate type of review, it is critical to know before embarking on a review project, why the research synthesis is conducted and what type of methods are best aligned with the pursued goals.

9.5. Concluding Remarks

In light of the increased use of evidence-based practice and research generating stronger evidence ( Grady et al., 2011 ; Lyden et al., 2013 ), review articles have become essential tools for summarizing, synthesizing, integrating or critically appraising prior knowledge in the eHealth field. As mentioned earlier, when rigorously conducted review articles represent powerful information sources for eHealth scholars and practitioners looking for state-of-the-art evidence. The typology of literature reviews we used herein will allow eHealth researchers, graduate students and practitioners to gain a better understanding of the similarities and differences between review types.

We must stress that this classification scheme does not privilege any specific type of review as being of higher quality than another ( Paré et al., 2015 ). As explained above, each type of review has its own strengths and limitations. Having said that, we realize that the methodological rigour of any review — be it qualitative, quantitative or mixed — is a critical aspect that should be considered seriously by prospective authors. In the present context, the notion of rigour refers to the reliability and validity of the review process described in section 9.2. For one thing, reliability is related to the reproducibility of the review process and steps, which is facilitated by a comprehensive documentation of the literature search process, extraction, coding and analysis performed in the review. Whether the search is comprehensive or not, whether it involves a methodical approach for data extraction and synthesis or not, it is important that the review documents in an explicit and transparent manner the steps and approach that were used in the process of its development. Next, validity characterizes the degree to which the review process was conducted appropriately. It goes beyond documentation and reflects decisions related to the selection of the sources, the search terms used, the period of time covered, the articles selected in the search, and the application of backward and forward searches ( vom Brocke et al., 2009 ). In short, the rigour of any review article is reflected by the explicitness of its methods (i.e., transparency) and the soundness of the approach used. We refer those interested in the concepts of rigour and quality to the work of Templier and Paré (2015) which offers a detailed set of methodological guidelines for conducting and evaluating various types of review articles.

To conclude, our main objective in this chapter was to demystify the various types of literature reviews that are central to the continuous development of the eHealth field. It is our hope that our descriptive account will serve as a valuable source for those conducting, evaluating or using reviews in this important and growing domain.

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• Published: 31 August 2024

Incidence of post-extubation dysphagia among critical care patients undergoing orotracheal intubation: a systematic review and meta-analysis

• Weixia Yu 1   na1 ,
• Limi Dan 1   na1 ,
• Jianzheng Cai 1 ,
• Yuyu Wang 1 ,
• Qingling Wang 1 ,
• Yingying Zhang 1 &
• Xin Wang 1  

European Journal of Medical Research volume  29 , Article number:  444 ( 2024 ) Cite this article

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Post-extubation dysphagia (PED) emerges as a frequent complication following endotracheal intubation within the intensive care unit (ICU). PED has been strongly linked to adverse outcomes, including aspiration, pneumonia, malnutrition, heightened mortality rates, and prolonged hospitalization, resulting in escalated healthcare expenditures. Nevertheless, the reported incidence of PED varies substantially across the existing body of literature. Therefore, the principal objective of this review was to provide a comprehensive estimate of PED incidence in ICU patients undergoing orotracheal intubation.

We searched Embase, PubMed, Web of Science, Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang Database, China Science, Technology Journal Database (VIP), and SinoMed databases from inception to August 2023. Two reviewers independently screened studies and extracted data. Subsequently, a random-effects model was employed for meta-statistical analysis utilizing the “meta prop” command within Stata SE version 15.0 to ascertain the incidence of PED. In addition, we performed subgroup analyses and meta-regression to elucidate potential sources of heterogeneity among the included studies.

Of 4144 studies, 30 studies were included in this review. The overall pooled incidence of PED was 36% (95% confidence interval [CI] 29–44%). Subgroup analyses unveiled that the pooled incidence of PED, stratified by assessment time (≤ 3 h, 4–6 h, ≤ 24 h, and ≤ 48 h), was as follows: 31.0% (95% CI 8.0–59.0%), 28% (95% CI 22.0–35.0%), 41% (95% CI 33.0–49.0%), and 49.0% (95% CI 34.0–63.0%), respectively. When sample size was 100 <  N  ≤ 300, the PED incidence was more close to the overall PED incidence. Meta-regression analysis highlighted that sample size, assessment time and mean intubation time constituted the source of heterogeneity among the included studies.

The incidence of PED was high among ICU patients who underwent orotracheal intubation. ICU professionals should raise awareness about PED. In the meantime, it is important to develop guidelines or consensus on the most appropriate PED assessment time and assessment tools to accurately assess the incidence of PED.

Graphical abstract

Introduction

Mechanical ventilation is the most common technological support, being required by 20–40% of adult in ICU [ 1 ]. Orotracheal intubation is the primary way of mechanical ventilation in ICU, which can increase the risk of post-extubation dysphagia (PED) [ 2 , 3 ]. PED is any form of swallowing dysfunction that arises subsequent to extubation following endotracheal intubation, affecting the passage of food from the entrance to the stomach. The occurrence rate of PED within the ICU setting demonstrates considerable variation among different countries [ 4 ]. The incidence varied among countries, including 13.3–61.8% in the United States [ 5 , 6 ], 25.3–43.5% in France, and 23.2–56% in China [ 7 , 8 ], and the incidence ranging from 7 to 80% [ 9 , 10 ]. Significantly, PED standing out as a prominent complication encountered in this particular context. For instance, See et al. have elucidated that patients afflicted with PED face an 11-fold higher risk of aspiration compared to those without PED [ 11 ]. McIntyre et al. have underscored that patients afflicted with PED endure double the length of stay in the ICU and the overall hospitalization period when compared to patients without PED [ 10 ]. Furthermore, it is essential to note that PED emerged as an independent predictor of 28-day and 90-day mortality [ 12 ]. This high incidence of PED places an immense burden not only on patients but also on the broader healthcare system. Therefore, a systematic review and meta-analysis is necessary to explore the incidence of PED in ICU patients. A systematic review and meta-analysis conducted by McIntyre et al. reported that the incidence of PED was 41%, but the main outcomes of their partly included studies was aspiration [ 12 ]. Although aspiration and PED are closely related, not all aspiration is caused by dysphagia. The incidence of aspiration was 8.80%-88.00% in ICU [ 13 , 14 ], so the incidence of PED in that study may be overestimated. Moreover, there has been increasing literature on PED of ICU patients, and a new systematic review and meta-analysis is needed to obtain a more precise estimate of its incidence.

The incidence of PED may indeed vary depending on various covariates, including assessment time, mean intubation time, age and other relevant factors. First, there is no standard time for swallowing function assessment, which spans a range of intervals, including 3 h [ 6 , 9 , 12 ], 4–6 h [ 15 , 16 ], 24 h [ 17 , 18 , 19 ], 48 h [ 20 ], 7 days [ 21 ], and discharge [ 22 ], and the incidence of PED was 80% [ 9 ], 22.62% [ 15 ], 56.06% [ 18 ], and 35.91% [ 20 ], 22.06% [ 21 ], and 28.78% [ 22 ], respectively. Second, the PED is closely tied to the time of orotracheal intubation. Skoretz et al. have demonstrated that the overall incidence of PED in the ICU ranges from 3 to 4%. However, upon re-analysis of patients subjected to orotracheal intubation for more than 48 h, the PED incidence can surge as high as 51% [ 23 ]. Third, the choice of assessment tool to evaluate PED in ICU patients plays a pivotal role. These assessment tools may include Video-fluoroscopic Swallowing Study (VFSS), Fiberoptic Endoscopic Evaluation of Swallowing (FEES), Standardized Swallowing Assessment (SSA), Bedside Swallowing Evaluation (BSE), Gugging Swallowing Screen (GUSS), Post-Extubation Dysphagia Screening Tool (PEDS), Water Swallowing Test (WST) and other assessment tools. FEES and VFSS are considered the gold standards, with a detection rate of approximately 80% [ 9 ]. SSA and BSE exhibit detection rates of 22% and 62%, respectively [ 5 , 15 ]. Finally, age-related changes in laryngeal sensory and motor functions also influence PED risk [ 24 ]. Notably, there may not be a significant difference in the incidence of PED between elderly and young patients within the initial 48 h post-extubation. However, elderly patients exhibit a significantly slower rate of PED recovery compared to their younger counterparts over time (5.0 days vs 3.0 days; p  = 0.006) [ 5 ]. Therefore, it is necessary to explore the potential source of heterogeneity in the incidence of PED in ICU patients from such covariates.

The purpose of this study was to estimate the incidence of PED among ICU patients who underwent orotracheal intubation and investigate potential sources of heterogeneity through the application of subgroup analyses and meta-regression.

This systematic review and meta-analysis was conducted adhering to the guidelines outlined in the Joanna Briggs Institute (JBI) Reviewers’ Manual and followed the principles of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 statement (PRISMA 2020) [ 25 ] (see Additional file 1: Table S1). In addition, it was registered with PROSPERO under the registration number CRD42022373300.

Eligibility criteria

The study’s eligibility criteria were established in accordance with the PICOS principle. Inclusion criteria as follows: population (P): adult patients (≥ 18 years old) admitted to the ICU who underwent orotracheal intubation. Exposure (E): undergoing orotracheal intubation. Outcome (O): PED. Study design (S): observational study (cohort, case–control, cross-sectional study). In studies where multiple articles were derived from the same sample, only the article providing the most detailed data was included. Patients at high risk of dysphagia (such as those with head and neck cancer, who have undergone head and neck surgery, patients receiving palliative care, esophageal dysfunction, stroke, esophageal cancer and Parkinson’s disease) were excluded. Studies were excluded if they exhibited incomplete original data or data that could not be extracted. Studied were also excluded if their sample sizes fell below 30 participants or the full text was inaccessible.

Data sources and search strategy

Our comprehensive search multiple databases, including Embase, PubMed, Web of Science, Cochrane Library, China National Knowledge Infrastructure (CNKI), Wanfang, China Science and Technology Journal Database (VIP), and SinoMed, with the search period encompassing inception to August 18, 2023. Search language was Chinese and English. The limited number of studies retrieved initially, primarily attributed to the inclusion of the qualifier “ICU” in the initial search, prompted us to broaden the scope of our literature search. Consequently, we refined the search strategy by reducing the emphasis on “ICU” during the search process. After a series of preliminary searches, we finalized the search strategy, which combined subject headings and free-text terms while employing Boolean operators to enhance search precision. In addition, a manual hand-search of the reference lists of selected articles was carried out to identify any supplementary studies not originally identified through the electronic search. For a detailed presentation of our complete search strategies across all databases, please refer to Additional file 1: Table S2.

Quality evaluation

The evaluation of the risk of bias within the included studies was conducted by two trained investigators. Cross-sectional study was evaluated by the Agency for Healthcare Research and Quality (AHRQ) tool [ 26 ], which consisted of 11 items, resulting in a maximum score of 11. Scores falling within the ranges of 0–3, 4–7, and 8–11 corresponded to studies of poor, moderate, and high quality, respectively. Cohort study was evaluated by the Newcastle–Ottawa Scale (NOS) tool [ 27 ], which comprised three dimensions and eight items, allowing for a star rating ranging from 2 to 9 stars. In this case, 0–4, 5–6, and 7–9 stars were indicative of study of poor, moderate, and high quality, respectively. Any discrepancies or disagreements between the investigators were resolved through discussion, when necessary, consultation with a third expert specializing in evidence-based practice methodology.

Study selection and data extraction

Bibliographic records were systematically exported into the NoteExpress database to facilitate the screening process and the removal of duplicate citations. Initial screening, based on titles and abstracts, was conducted by two reviewers who possessed specialized training in evidence-based knowledge. To ascertain whether the studies satisfied the predefined inclusion and exclusion criteria, the full texts of potentially relevant articles were acquired. In the event of disagreements between the two reviewers, resolution was achieved through discussion or, when necessary, by enlisting the input of a third reviewer for arbitration.

After confirming the included studies, the two authors independently extracted data from the each paper, including the first author, year of publication, country, study design, ICU type, mean patient age, mean intubation time, assessment time, assessment tool, evaluator, sample size, and the PED event. Any disparities during the process of extracted data were addressed through thorough discussion and consensus-building among the reviewers.

The outcomes of this review were as follows: (1) incidence of PED in patients with orotracheal intubation in the ICU; (2) sources of heterogeneity of PED in patients with orotracheal intubation in ICU.

Statistical analyses

Meta-analysis was conducted using the ‘meta prop’ function from the meta package within STATA/SE (version 15.0, StataCorp, TX, USA). To approximate the normal distribution of the data, incidence estimates were transformed using the “Freeman-Tukey Double Arcsine Transformation”. Heterogeneity was assessed using the I 2 statistic, and pooled analyses of PED were executed employing a random-effects model in the presence of significant heterogeneity ( I 2  ≥ 50%), with fixed-effects models utilized when heterogeneity was non-significant. A significance level of P  < 0.05 was established for all analyses.

Subgroup analyses were undertaken to investigate the potential impact of various factors, including assessment tool (gold standard, SSA, GUSS, BSE, PEDS, WST, and other assessment tools), year of publication (2000–2010, 2011–2015, 2016–2020, 2021–2023), study design (cross-sectional study and cohort study), study quality (moderate quality and high quality), assessment time (≤ 3 h, 4–6 h, ≤ 24 h, ≤ 48 h, and after 48 h post-extubation), mean intubation time (≤ 24 h, 48 – 168 h, and > 168 h), mean patient age (≤ 44 years, 45–59 years, 60–74 years), evaluator (nurses, speech-language pathologist), ICU type (Trauma ICU, Cardiac surgery ICU, Mixed medical and surgical ICU), and sample size ( N  ≤ 100, 100 <  N  ≤ 200, 200 <  N  ≤ 300, N  > 300) on the pooled estimate. In instances where no source of heterogeneity was identified in the subgroup analyse, we conducted meta-regression to further pinpoint the origins of heterogeneity, focusing on assessment time, mean intubation time, mean age, assessment tool, sample size, evaluator, ICU type, study design, study quality and year of publication. Sensitivity analysis by the “leave-one-out method” was employed to evaluate the random-effects model’s stability of the pooled incidence of PED. Publication bias was assessed by funnel plot and “Trim and Full” method.

Certainty of the evidence

The level of evidence was assessed using the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) [ 28 ]. This tool classifies the certainty of evidence into four levels: very low, low, moderate, and high. “High quality” suggests that the actual effect is approximate to the estimate of the effect. On the other hand, “Very low quality” suggests that there is very little confidence in the effect estimate and the reported estimate may be substantially different from what was measured. Two reviewers judged the following aspects: risk of bias, inconsistency, imprecision, indirect evidence, and publication bias. Disagreements were resolved by consensus with the third reviewer.

Study selection

Out of the 4144 studies initially identified, 1280 duplicate studies were removed, and an additional 2864 studies that were deemed irrelevant were excluded based on title and abstract screening. Subsequently, a thorough examination of the full text was conducted for the remaining 122 studies. A manual hand-search of the reference lists of selected articles was 5 studies. Finally, 30 studies were chosen as they met the predetermined inclusion criteria for this systematic review and meta-analysis. The study selection flowchart is shown in Fig.  1 .

Flowchart of study selection

General characteristics of the included studies

The characteristics of the included studies are shown in Table  1 . The total sample size across these studies amounted to 6,228 participants. The earliest study in this review was conducted in 2003 [ 29 ], while the most recent study was conducted in 2023 [ 15 ], with 14 studies published after 2020. The study with the largest sample size was conducted by Schefold et al. [ 12 ], comprising 933 participants, while the study with the smallest sample size was carried out by Yılmaz et al. [ 19 ], including 40 participants. The methods employed to assess the incidence of PED exhibited variability among the studies. Specifically, one study employed VFSS [ 30 ], and four studies relied on FEES [ 9 , 29 , 31 , 32 ], and seven studies utilized SSA assessment tools [ 7 , 15 , 16 , 33 , 34 , 35 , 36 ]. Furthermore, six studies utilized BSE [ 5 , 10 , 17 , 37 , 38 , 39 ], two studies employed WST [ 12 , 40 ], two studies adopted PEDS [ 8 , 18 ], two studies utilized GUSS [ 19 , 41 ], and six studies employed other assessment tools [ 6 , 20 , 21 , 22 , 43 ,, 42 , 43 ] such as ASHA, FOIS, SSQ200, NPS-PED, MASA, and YSP.

Among all the studies, 23 studies recorded the assessment time for PED. Specifically, three studies assessed PED within ≤ 3 h post-extubation [ 6 , 9 , 12 ], four studies conducted assessments at 4–6 h post-extubation [ 15 , 16 , 33 , 36 ], nine studies assessed PED within ≤ 24 h post-extubation [ 7 , 8 , 17 , 18 , 19 , 31 , 34 , 40 , 41 ], three studies assessed PED within ≤ 48 h post-extubation [ 5 , 20 , 37 ], and four studies evaluated PED at > 24 h post-extubation [ 21 , 22 , 29 , 38 ]. In terms of study quality, eight of the included studies were categorized as high quality, while the remainder were deemed of moderate quality (see Additional 1: Tables S3, S4).

Meta-analysis results

Utilizing the random-effects model, the pooled incidence of PED was estimated to be 36% (95% CI 29.0%–44.0%, I 2  = 97.06%, p  < 0.001; Fig.  2 ), indicating a substantial degree of heterogeneity. Despite conducting additional subgroup analyses, the source of this high heterogeneity remained elusive. However, the results of the meta-regression analysis revealed that sample size ( p  < 0.001), assessment time ( p  = 0.027) and mean intubation time ( p  = 0.045) emerged as the significant factor contributing to the heterogeneity.

Overall pooled incidence of PED in ICU

Subgroup analysis of incidence

The subgroup analyses yielded the following incidence rates of PED based on assessment time post-extubation: the incidence of PED within 3 h post-extubation was 31% (95% CI 8.0–59.0), 4–6 h was 28% (95% CI 22.0–35.0, I 2  = 78.56%, p  < 0.001), within 24 h was 41% (95% CI 33.0–49.0, I 2  = 88.99%, p  < 0.001), and within 48 h was 49%. In addition, the incidence of PED beyond 24 h post-extubation was 37% (95% CI 23.0–52.0, I 2  = 91.73%, p  < 0.001) (Additional file 1: Fig. S1). Furthermore, when analyzing studies based on sample size ( N ), the overall incidence of PED was found 51% (95% CI 39.0–63.0, I 2  = 87.11%, p  < 0.001) for studies with N  < 100 participants, 37% (95% CI 31.0–43.0, I 2  = 84.74%, p  < 0.001) for studies with 100 <  N  ≤ 200 participants, 32% (95% CI 20.0–46.0, I 2  = 97.16%, p  < 0.001) for studies with 200 <  N  ≤ 300 participants, and 16% (95% CI 8.0–26.0, I 2  = 97.07%, p  < 0.001) for studies with N  > 300 participants (see Additional file 1: Fig. S2). In addition, further analyses were conducted based on assessment tool, mean intubation time, mean age, ICU type, evaluator, publication year, study design and study quality (see Additional file 1: Figs. S3–S11).

Results of meta-regression analysis

In the meta-regression analysis, we examined PED assessment time, sample size, assessment tools, mean intubation time, mean age, ICU type, evaluator, publication year, study design and study quality as potential covariates to identify the source of heterogeneity (Table  2 ). The univariate meta-regression analysis revealed a statistically significant correlation between incidence and sample size, assessment time and mean intubation time. Bubble plots of meta-regression of covariates were shown in Additional (see Additional file 1: Figs. S12–S22).

Sensitivity analysis

Sensitivity analysis showed that the incidence of PED ranged from 29 to 44% (see Additional file 1: Fig. S23). The marginal variance between these results and the pooled incidence was minimal, suggesting that the result of the pooled incidence being stable and reliable.

Publication bias

In our study, publication bias was detected by the funnel plot (see Additional file 1: Fig. S24). We found that the adjusted effect size was similar to the original effect size ( p  < 0.01) (see Additional file 1: Fig. S25).

The certainty of evidence was very low for all comparisons performed according to the GRADE rating [ 28 ]. Thus, it can be considered that the certainty of the evidence regarding the incidence of PED in this review is very low (Table  3 ).

This systematic review and meta-analysis aimed to estimate the incidence of PED in ICU patients. The study revealed an overall incidence of PED in ICU patients who underwent orotracheal intubation to be 36.0%. This incidence rate was comparable to the incidence of dysphagia resulting from stroke (36.30%) [ 45 ] and aligned with the incidence of PED observed in ICU patients (36%) [ 46 ]. However, it was slightly lower than the 41% reported in the meta-analysis conducted by McIntyre et al. [ 4 ]. The incidence of PED among ICU patients who underwent orotracheal intubation was high, ICU medical professionals, especially nurses should raise awareness about PED. However, the included studies were characterized by diversity and heterogeneity in assessment time and assessment tools signaled the need for obtaining consensus on a range of issues, including assessment time and assessment tools appropriate for ICU.

Sample size

This review identified sample size as a significant source of heterogeneity ( p  < 0.001). Notably, the incidence of PED demonstrated a gradual decrease as the sample size of the studies increased. In larger scale studies, such as those conducted by McIntyre et al. and Schefold et al., simpler assessment tools are employed, allowing for quick completion [ 10 , 12 ]. However, the reliability and validity of some of these tools remain unverified. Conversely, certain studies are conducted by highly trained professionals using the gold standard for PED assessment [ 9 , 29 , 31 ], which, while more accurate, is also time-consuming and costly [ 47 ]. In addition, some ICU patients, due to their unstable conditions, are unable to complete the gold standard assessment, resulting in relatively smaller sample sizes for these studies.

In statistics, sample size is intricately linked to result stability, and the confidence intervals for subgroups with N  < 100 in this study exhibited a wider range, this might diminish the result precision and lead to larger deviations from the true value. However, as the sample size increased to 100 <  N  ≤ 300, the confidence intervals narrowed in comparison to other subgroups. Consequently, when sample size was 100 <  N  ≤ 300, the PED incidence rates were more close with the overall PED rate. According to the central limit theorem, if the sampling method remains consistent, results obtained from larger samples are more stable and closer to the true value [ 48 , 49 ]. It is worth noting that the confidence intervals for the subgroup with N  > 300 in this study were wider and demonstrated a larger divergence from the total PED incidence. Therefore, in future studies, careful consideration of the sample size, based on the detection rate of the assessment tool used, is advisable to ensure both the stability and reliability of the results.

Mean intubation time

This review identified mean intubation time as a significant source of heterogeneity ( p  = 0.045). Variances in mean intubation time among ICU patients undergoing orotracheal intubation can lead to differing degrees of mucosal damage in the oropharynx and larynx [ 2 , 50 ], thereby resulting in varying incidence rates of PED. For instance, Malandraki et al. have reported that prolonged intubation is associated with more than a 12-fold increased risk of moderate/severe dysphagia compared to shorter intubation durations, and this effect is particularly pronounced among elderly patients [ 51 ]. Moreover, studies have demonstrated that ICU patients with extended orotracheal intubation periods leading to PED also exhibit diminished tongue and lip strength, protracted oral food transportation, slower swallowing, and muscle weakness in swallowing-related muscles [ 24 , 46 ]. In view of these findings, ICU medical professionals should routinely evaluate the need for orotracheal intubation, strive to minimize the duration of mechanical ventilation.

PED assessment time

This review identified assessment time as a significant source of heterogeneity ( P  = 0.027). It is important to note that there are currently no established guidelines recommending the optimal timing for the initial assessment of PED in ICU patients who have undergone orotracheal intubation. Consequently, the assessment time varies widely across studies, resulting in PED incidence rates ranging from 28 to 49% among subgroups. Interestingly, the incidence of PED assessed within ≤ 3 h post-extubation appeared lower than that assessed within ≤ 24 h and ≤ 48 h post-extubation. This difference may be attributed to the study by Schefold et al., which featured a shorter intubation duration [ 12 ]. Therefore, the incidence of PED assessed within ≤ 3 h post-extubation in ICU patients with orotracheal intubation may be underestimated. Moreover, it is essential to highlight that some ICU patients, particularly those with severe illnesses and extended intubation time, may face challenges in complying with post-extubation instructions provided by healthcare personnel. Paradoxically, this group of patients is at a higher risk of developing PED, subsequently increasing their susceptibility to post-extubation pneumonia [ 11 ]. ICU professionals should evaluate swallowing function in patients post-extubation; early identification of patients at risk for PED to reduce complications. If PED is identified, nurses should follow-up assessments at multiple time to obtain a thorough comprehension of PED recovery trajectory among PED patients, which can serve as a foundation for determining the timing of clinical interventions accurately.

PED assessment tools

Despite the subgroup analyses and meta-regression results indicating that PED assessment tools did not contribute to the observed heterogeneity, it is important to acknowledge the wide array of assessment tools employed across the studies included in this review. The study’s findings revealed that the results of the GUSS and BSE assessments were most closely aligned with the gold standard screening results. In contrast, the PEDS assessment results tended to be higher than those derived from the gold standard assessment. Furthermore, the results of other assessment tools generally yielded lower incidence rates of PED, possibly attributable to variations in specificity or sensitivity. FEES and VFSS assessments are recognized for their meticulous scrutiny of patients’ swallowing processes, including the detection of food residue and aspiration, which may not be as comprehensively addressed by other assessment methods [ 51 ]. Assessment tools such as BSE, SSA, GUSS, WST, and other clinical methods do not provide direct visualization of the swallowing process. Instead, assessors rely on the observation of overt clinical symptoms during the patient’s initial food or water intake to judge the presence of PED. However, these methods may overlook occult aspiration in patients, potentially resulting in an underestimation of PED incidence. In contrast, PEDS, which primarily assesses patients based on their medical history and plumbing symptoms without screening for drinking or swallowing, may overestimate PED incidence. Considering the varying strengths and limitations of existing assessment tools, ICU professionals select appropriate PED assessment tool based on the characteristics of the critically ill patient. Early and rapid identification of PED, before the use of more complex and expensive assessment tools, minimizes the occurrence of complications in patients.

Strengths and weaknesses

In this study, we conducted a comprehensive analysis of the incidence of PED in ICU patients who underwent orotracheal intubation across various subgroups, revealing a notable degree of heterogeneity among the included studies. In our study, we have expanded the search as much as possible and included a total of 30 papers after screening, half of which were published after 2020. There are several limitations that should be considered when interpreting the results of this meta-analysis. First, there was varied heterogeneity between methodological of the study and estimates of prevalence that may question the appropriateness of calculating pooled prevalence estimates. However, in order to address this heterogeneity, we addressed the heterogeneity with applying a random-effect model and conducting subgroup analysis and meta-regression to explore three sources of heterogeneity. Second, the overall quality of evidence for the incidence of PED was rated as low according to GRADE. Higher quality original studies on the incidence of PED should be performed in the future. As a result, the findings should be interpreted with caution in such cases.

In conclusion, our systematic review and meta-analysis revealed a high incidence of PED among ICU patients who underwent orotracheal intubation. It is also worth noting that the incidence of PED in the ICU may be underestimated. It is expected to increase awareness about the issue of PED among ICU patients. It will be important to develop guidelines or consensus on the most appropriate PED assessment time and assessment tools to accurately assess the incidence of PED.

Relevance to clinical practice

Each year, a substantial number of critically ill patients, ranging from 13 to 20 million, necessitate endotracheal intubation to sustain their lives. Patients undergoing orotracheal intubation are at heightened risk of developing PED. PED has been linked to prolonged hospital and ICU length of stay, increased rates of pneumonia, and all-cause mortality. Early identification of high-risk patients by clinical nurses is critical for reduce patient burden and adverse outcomes.

Early and multiple times assessment: Future investigations should early assess PED in clinical practice, especially within 6 h post-extubation. Furthermore, we suggest for follow-up assessments at multiple time to obtain a thorough comprehension of PED incidence and the recovery trajectory among ICU patients who have undergone orotracheal intubation.

Assessment tool: Considering the varying strengths and limitations of existing assessment tools, ICU professionals should carefully evaluate the characteristics of critically ill patients and select appropriate assessment tools, before the use of more complex and expensive assessment tools.

Routinely evaluate the need for orotracheal intubation: Healthcare professionals should routinely evaluate the need for orotracheal intubation, strive to minimize the duration of mechanical ventilation.

Availability of data and materials

All data related to the present systematic review and meta-analysis are available from the original study corresponding author on reasonable request.

Abbreviations

Confidence interval

• Intensive care unit

Post-extubation dysphagia

Sydney Swallow Questionnaire 200

Water swallowing test

Post-Extubation Dysphagia Screening Tool

Bedside swallow evaluation

The Yale swallow protocol

Mann Assessment of Swallowing Ability

American Speech-Language-Hearing Association

Video Fluoroscopic Swallowing Study

Fiberoptic endoscopic evaluation of swallowing

Gugging swallowing screen

Standardized Swallowing Assessment

Functional Oral Intake Scale

Nurse-performed screening for post-extubation dysphagia

Speech-language pathologists

Events of PED

Preferred Reporting Items for Systematic Reviews and Meta-analyses

International Prospective Register of Systematic Reviews

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Weixia Yu, Limi Dan, Jianzheng Cai, Yuyu Wang, Qingling Wang, Yingying Zhang & Xin Wang

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Weixia Yu, Limi Dan, Jianzheng Cai, and Yuyu Wang developed the original concept of this systematic review and meta-analysis. Weixia Yu, Limi Dan, Jianzheng Cai and Yuyu Wang contributed to the screening of eligible studies, data extraction, and data synthesis. Weixia Yu, Limi Dan, Jianzheng Cai, Yuyu Wang and Qingling Wang drafted the first version of the manuscript. Yingying Zhang, Qingling Wang and Xin Wang prepared the tables and figures. All the authors have edited and contributed for intellectual content. All the authors read and approved the final manuscript and take public responsibility for it.

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Additional file 1: Table S1. PRISMA 2020 Checklist. Table S2. Search strategy. Table S3. Quality evaluation results of the cohort studies. Table S4. Quality evaluation results of the cross-sectional study. Fig. S1. Subgroup analysis of the incidence of PED by assessment time. Fig. S2. Subgroup analysis of the incidence of PED by sample size. Fig. S3. Incidence of PED by assessment tool. Fig. S4. Incidence of PED by mean intubation time. Fig. S5 Incidence of PED by mean age. Fig. S6. Incidence of PED by ICU type. Fig. S7. Incidence of PED by evaluator. Fig. S8. Incidence of PED by year of publication. Fig. S9. Incidence of PED by study design. Fig. S10. Incidence of PED by quality of cohort study. Fig. S11. Incidence of PED by quality of Cross-sectional study. Fig. S12. Bubble plot of meta-regression result for evaluate time as a covariate. Fig. S13. Bubble plot of meta-regression result for sample size as a covariate. Fig. S14. Bubble plot of meta-regression result for assessment tool as a covariate. Fig. S15. Bubble plot of meta-regression result for mean intubation time as a covariate. Fig. S16. Bubble plot of meta-regression result for mean age as a covariate. Fig. S17. Bubble plot of meta-regression result for ICU type as a covariate. Fig. S18. Bubble plot of meta-regression result for evaluator as a covariate. Fig. S19. Bubble plot of meta-regression result for year of publication as a covariate. Fig. S20. Bubble plot of meta-regression result for study design as a covariate. Fig. S21. Bubble plot of meta-regression result for quality of cohort study as a covariate. Fig. S22. Bubble plot of meta-regression result for quality of cross-sectional study as a covariate. Fig. S23. Sensitivity analysis of PED. Fig. S24. Publication bias assessment plot. Fig. S25. Publication bias assessment plot. “Trim and Full test” method.

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Yu, W., Dan, L., Cai, J. et al. Incidence of post-extubation dysphagia among critical care patients undergoing orotracheal intubation: a systematic review and meta-analysis. Eur J Med Res 29 , 444 (2024). https://doi.org/10.1186/s40001-024-02024-x

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Competitive advantages of sustainable startups: systematic literature review and future research directions.

1. Introduction

2. materials and methods, 2.1. stage 1—identification: searching the databases, 2.2. stage 2—screening: elimination of duplicates and linguistic adjustment, 2.3. stage 3—eligibility: analysis of titles, keywords, and abstracts, 2.4. stage 4—inclusion: detailed analysis and selection of articles.

• Identification of the study: title of the article, authors, and year of publication;
• Background: a brief description of the research problem;
• Objectives of the study: main objective of the article;
• Methodology: description of the research methods used;
• Sample and data: sample size, source, and types of data;
• Results: main findings of the study;
• Limitations of the study: limitations or biases identified by the authors;
• Contribution to the literature review: relation of the article to the present research;
• Summary and conclusions: general conclusions of the study;
• Additional comments: study quality, research relevance, and possible gaps.

3. Results and Discussion

3.1. descriptive analysis, 3.1.1. annual frequency of publications, 3.1.2. distribution by journal, 3.1.3. main authors, 3.1.4. co-authorship analysis, 3.1.5. countries analysis, 3.1.6. keyword analysis, 3.1.7. research methodologies, 3.2. content analysis, 3.2.1. competitive advantages of sustainable startups, 3.2.2. impact of competitive advantages on the esg perspective of sustainable startups, environmental perspective, social perspective, governance perspective, 3.2.3. future research directions on the competitive advantages of sustainable startups, economic–environmental balance in sustainable startups, impact of public policies and regional contexts, innovation, sustainability, and business models, the role of investors and market dynamics, startup performance and sustainability, 4. conclusions, supplementary materials, author contributions, institutional review board statement, informed consent statement, data availability statement, conflicts of interest.

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Martins de Souza, A.; Puglieri, F.N.; de Francisco, A.C. Competitive Advantages of Sustainable Startups: Systematic Literature Review and Future Research Directions. Sustainability 2024 , 16 , 7665. https://doi.org/10.3390/su16177665

Martins de Souza A, Puglieri FN, de Francisco AC. Competitive Advantages of Sustainable Startups: Systematic Literature Review and Future Research Directions. Sustainability . 2024; 16(17):7665. https://doi.org/10.3390/su16177665

Martins de Souza, Adriano, Fabio Neves Puglieri, and Antonio Carlos de Francisco. 2024. "Competitive Advantages of Sustainable Startups: Systematic Literature Review and Future Research Directions" Sustainability 16, no. 17: 7665. https://doi.org/10.3390/su16177665

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• Review Article
• Published: 04 September 2024

Neurovascular structure-adjacent frozen-section examination (NeuroSAFE) during robot-assisted radical prostatectomy: a systematic review and meta-analysis of comparative studies

• Francesco Ditonno   ORCID: orcid.org/0009-0005-0126-4731 1 , 2 ,
• Eugenio Bologna   ORCID: orcid.org/0000-0002-1140-0590 1 , 3 ,
• Leslie Claire Licari 1 , 3 ,
• Antonio Franco 1 , 4 ,
• Donato Cannoletta 5 ,
• Enrico Checcucci   ORCID: orcid.org/0000-0001-7901-5608 6 ,
• Alessandro Veccia   ORCID: orcid.org/0000-0001-5947-3206 2 ,
• Riccardo Bertolo   ORCID: orcid.org/0000-0003-0260-4601 2 ,
• Simone Crivellaro 5 ,
• Francesco Porpiglia 7 ,
• Cosimo De Nunzio   ORCID: orcid.org/0000-0002-2190-512X 4 ,
• Alessandro Antonelli   ORCID: orcid.org/0000-0002-7455-8803 2 &
• Riccardo Autorino   ORCID: orcid.org/0000-0001-7045-7725 1  

Prostate Cancer and Prostatic Diseases ( 2024 ) Cite this article

Metrics details

• Cancer therapy
• Outcomes research

To compare surgical, pathological, and functional outcomes of patients undergoing NeuroSAFE-guided RARP vs. RARP alone.

In February 2024, a literature search and assessment was conducted through PubMed ® , Scopus ® , and Web of Science ™ , to retrieve data of men with PCa (P) undergoing RARP with NeuroSAFE (I) versus RARP without NeuroSAFE (C) to evaluate surgical, pathological, oncological, and functional outcomes (O), across retrospective and/or prospective comparative studies (Studies). Surgical (operative time [OT], number of nerve-sparing [NS] RARP, number of secondary resections after NeuroSAFE), pathological (PSM), oncological (biochemical recurrence [BCR]), and functional (postoperative continence and sexual function recovery) outcomes were analyzed, using weighted mean difference (WMD) for continuous variables and odd ratio (OR) for dichotomous variables.

Overall, seven studies met the inclusion criteria (one randomized clinical trial, one prospective non-randomized trial and five retrospective studies) and were eligible for SR and MA. A total of 4,207 patients were included in the MA, with 2247 patients (53%) undergoing RARP with the addition of NeuroSAFE, and 1 960 (47%) receiving RARP alone. The addition of NeuroSAFE enhanced the likelihood of receiving a nerve-sparing (NS) RARP (OR 5.49, 95% CI 2.48–12.12, I 2  = 72%). In the NeuroSAFE cohort, a statistically significant reduction in the likelihood of PSM at final pathology (OR 0.55, 95% CI 0.39–0.79, I 2  = 73%) was observed. Similarly, a reduced likelihood of BCR favoring the NeuroSAFE was obtained (OR 0.47, 95% CI 0.35–0.62, I 2  = 0%). At 12-month postoperatively, NeuroSAFE led to a significantly higher likelihood of being pad-free (OR 2.01, 95% CI 1.25–3.25, I 2  = 0%), and of erectile function recovery (OR 3.50, 95% CI 2.34–5.23, I 2  = 0%).

Available evidence suggests that NeuroSAFE might represent a histologically based approach to NVB preservation, broadening the indications of NS RARP, reducing the likelihood of PSM and subsequent BCR. In addition, it might translate into better functional postoperative outcomes. However, the current body of evidence is mostly derived from non-randomized studies with a high risk of bias.

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Sheets containing raw data (extracted variables, statistical analyses) are available upon reasonable request from the corresponding author.

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Conception and design: Autorino, Ditonno; Acquisition of data: Franco, Cannoletta, Licari; Statistical analysis: Ditonno, Bologna; Interpretation of the data: Veccia, Bertolo, Checcucci, Crivellaro, Porpiglia, De Nunzio, Antonelli; Drafting of the manuscript: Ditonno; Critical revision of the manuscript for important intellectual content: Bologna, Licari, Franco, Cannoletta, Checcucci, Veccia, Bertolo, Crivellaro, Porpiglia, De Nunzio, Antonelli, Autorino Supervision: Autorino; Final approval of the version to be published: Ditonno, Bologna, Licari, Franco, Cannoletta, Checcucci, Veccia, Bertolo, Crivellaro, Porpiglia, De Nunzio, Antonelli, Autorino; Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved: Ditonno, Bologna, Licari, Franco, Cannoletta, Checcucci, Veccia, Bertolo, Crivellaro, Porpiglia, De Nunzio, Antonelli, Autorino; All authors read and approved the final version of the manuscript.

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Challenges in coffee fermentation technologies: bibliometric analysis and critical review

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• Valeria Hurtado Cortés   nAff1 ,
• Andrés Felipe Bahamón Monje   ORCID: orcid.org/0000-0002-2620-148X 1 ,
• Jaime Daniel Bustos Vanegas   nAff1 &
• Nelson Gutiérrez Guzmán   nAff1  

Advancements in coffee processing technologies have led to improved efficiency in field operations, but challenges still exist in their practical implementation. Various alternatives and solutions have been proposed to enhance processing efficiency and address issues related to safety, standardization, and quality improvement in coffee production. A literature review using SciMAT and ScientoPy software highlighted advancements in fermentation tanks and the emergence of novel fermentation methodologies. However, these innovations lack sufficient scientific evidence. Researchers are now focusing on systematic approaches, such as controlled fermentations and evaluating the influence of microorganisms and process conditions on sensory attributes and coffee composition. Brazil is the leader in coffee bean fermentation research, but the number of published papers in the field has recently decreased. Despite this, efforts continue to improve process control and optimize product quality. The study emphasizes the need for further innovation in coffee fermentation technologies to increase efficiency, sustainability, and profitability while minimizing environmental impact. Implementing these advancements promises a more sustainable and quality-driven future for the coffee industry.

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Introduction

Coffee is a crucial agricultural product and a popular beverage globally. Its growing popularity has led to the need for improved processes to enhance cup quality. The coffee fruit, also known as almond or green coffee, is composed of five layers that protect the endosperm. These layers, known as pulp, mucilage, parchment, and epidermis, form the endosperm and are subjected to roasting to form the flavor and aroma of the coffee drink.

The processing of coffee fruit involves stages to preserve the quality of the almond, which is then subjected to roasting. The types of processing include dry, semi-dry, and wet (de Melo Pereira et al. 2015 ). Dry processing involves pulping, fermentation, washing, drying, threshing, and roasting. Semi-dry processing involves mechanical removal of the exocarp and part of the mucilage, while wet processing involves drying and threshing.

Green coffee, obtained after processing, varies according to agro-climatological characteristics, species, variety, processing type, and post-harvest operations. Control of these operations is essential to preserve grain quality and maintain the consistency of its sensory profile.

Coffee fermentation is a metabolic process that converts sugars into energy and compounds through the action of enzymes in mucilage (Silva et al. 2013 ). This process involves the pulped coffee mass being kept in closed containers for 12 to 72 h to remove the mesocarp (mucilage) attached to the parchment. The mucilage, composed of simple sugars and a pectic substrate, is degraded into alcohols and organic acids by microorganisms, such as yeasts and bacteria (Correa et al. 2014 ; Pereira et al. 2016b ).

Coffee fermentation is a metabolic process that converts sugars into energy and compounds through the action of enzymes in mucilage. This process involves the pulped coffee mass being kept in closed containers for 12 to 72 h to remove the mesocarp (mucilage) attached to the parchment. The mucilage, composed of simple sugars and a pectic substrate, is degraded into alcohols and organic acids by microorganisms, such as yeasts and bacteria (Bressani et al. 2021b ).

Metabolites diffuse through parchment and endosperm, potentially causing exosmosis during fermentation until chemical potential equilibrium is achieved. The decrease in pH causes mucilage degradation, which can be removed by washing with water. Controlled fermentation can produce beverages with special aromas and flavors, such as sweet, citrus, and fruity.

Mucilage removal can be performed using mechanical or enzymatic methods, such as mechanical abrasion in ELMU-type mucilage removal machines and enzymes like Ultrazym 100, Irgazim 100, Benefax, and Cofepec. Recent research has revealed that the microbial degradation process during fermentation leads to physical and chemical changes in almonds, impacting the sensory characteristics of the resulting drink (da Mota et al. 2020 ; Elhalis et al. 2021 ).

Factors affecting reaction rates during coffee fermentation include temperature, water availability, fermentation time, and fruit maturity index. Devices designed for the operation must allow control and measurement of these factors to standardize the process.

This article shows the advances achieved over time with the technologies and methods used in the fermentation of coffee, taking into account the improvement in the processes of safety, standardization and quality of coffee. A bibliographic analysis of research focused on technologies and representative authors with related publications, among other aspects, was carried out. All with the purpose of observing the progress in the fermentation process with the objective of continuing researching and looking for solutions to obtain efficient and quality processing.

Search methodology

A bibliometric analysis was conducted on coffee bean fermentation publications to identify trends, emerging research directions, and relationships with fermenters and process variables, using Scopus database and ScientoPy and SciMAT software.

Databases, keywords and search criteria

This study analyzed data from the Scopus database on coffee, bean, and fermentation from 2001 to 2022, focusing on top countries, document types, and institutions, and downloaded in .CSV format for ScientoPy and SciMAT software.

Analysis using ScientoPy software

The downloaded data from Scopus were then loaded and processed with ScientoPy and the pre-processing results are presented in Table  1 . The journals and keywords categories were analyzed with the software to know the most relevant issues, total documents published by journal and keywords and evolution of them in the period from 2001 to 2022.

Analysis using SciMAT software

The data was preprocessed in modules “Knowledge base” and “Group sets” to remove duplicates and related keywords. The analysis was set to three periods (2001–2017, 2018–2020, and 2021–2022) and parameters were selected in “Analysis” to create evolution maps, strategic diagrams, and clusters.

Search results

Trends in publications over time.

The search for 231 documents from 2001 to 2022 revealed a stable trend in published documents. Between 2012 and 2022, there was a decrease in publications (Fig.  1 A and B). The top five countries were Brazil, followed by Indonesia, China, South Korea, and Colombia (Fig.  1 C). The majority of documents were articles, with a small percentage of reviews. The Universidade Federal de Lavras leads the list with 26 publications on the search topic, followed by Brazilian Universidade Federal do Parana (Fig.  1 -D). Indonesian institutions Hasanuddin University and Universitas Sylah Kuala also appear in the top 10. Nestlé S.A. ranks sixth in the top ten.

Documents published in the search topic (Graphs extracted from Scopus online database). ( A ) Documents published by year ( B ) Documents published by type ( C ) Documents published by country ( D ) Documents published by institution

There is no clear trend in the number of publications in the top 10 journals over time. Food Research International and IOP Conference Series: Earth and Environmental Science had the largest publications in 2020 and 2021 respectively. The evolution of the top 10 keywords is showed in Fig.  2 . This graph corroborates the main terms used and shows an increase over time of this words. After “Coffee”, which is a general term, “Fermentation” term has the highest number of documents published in the period analyzed, but according to the percentage of documents published in the last year 2021–2022 graph, “coffee fermentation” had the highest value (42.1%) in comparison to the other terms, which indicates that in the last year, this topic has had a higher relative growth.

Keywords in research related to the search topic ( A ) Cloud diagram of the top 1000 words ( B ) Evolution graph of the top 10 words

Although in general the interest in the fermentation process of coffee remains constantly growing, the topics addressed are diverse, which can be evidenced in the variety of key terms that the search throws up. Figure  2 -A shows the cloud of words specifically related to the fermentation process, such as types of fermentation, process control, variables involved, and fermenters. In relation to the latter, only two specific terms about it appear in the cloud, “bioreactors” and “bioreactor”; and some terms related with variables, control process or devices such as “controlled fermentation”, “temperature distribution”, ohmic technology”, “ohmic heating”.

Besides, some differences are obtained with the processing of data in SciMAT (Table  2 ), since this tool allows groups conformations in similar words and documents not related with the topic, however, words like “Fermentation” and “Coffee” remains as main terms, which is expected since these are general terms. Respect to the journals, the results are similar with some exceptions.

Topic evolution map and strategic diagram and cluster’s network

Figure  3 shows the graphs generated by SciMAT from the analysis of the data associated with the search string. According to the evolution map (Figs.  3 -1), for period 2001–2017 it can be observed nine main terms: “bacteria”, “coffee aroma”, “metabolomics”, “arabica”, “fungal fermentations”, “beverages”, “microorganisms”, “types of fermentation”, and “coffee”. In the period 2018–2020, the number of relevant terms increase to eleven, and only “microorganisms”, “coffee” and “type of fermentation” terms remain. New terms are included such as “classification”, “genetics”, “bacillus”, “yeast”, “seeds”, “sensory analysis” and “volatiles”. With respect to period 2020–2022, “bioreactors and process variables” term appears for the first time and there are new terms, for instance, analytical techniques as “spectrometry” and “chromatography”.

( 1 ) Evolution map of the relevant terms regarding the search topic in the documents reported from 2001 to 2022, and relevant relationships on evolution map. The color lines represent the main associations found, and ( 2 ) Strategic diagram associated with topic of interest for period ( A ) 2001–2017, ( B ) 2018–2020, ( C ) 2021–2022. ( 3 ) Cluster of terms associated with topic of interest for period ( A ) 2001–2017, ( B ) 2018–2020, ( C ) 2021–2022

With respect to the relevant associations shown on the evolution map (Figs.  3 -1), it is possible to observe terms associated with the study of microorganisms (relationships highlighted in red), such as bacteria, especially of the genus Bacillus, fungal fermentation, mainly related to yeasts, and lactic acid fermentation. These terms, in turn, present associations with parameters such as sensory analysis and volatiles. The latter is related to “bioreactor and process variables” in the last period. The term “bioreactor and process variables” is backward associated with “coffee”, a general term, and “types of fermentation”, which, in turn, is associated with “coffee aroma” (relationships highlighted in blue). These associations are anticipated due to the disparate processing methodologies, where the conditions of the process, the utilization of starter cultures, the type of microorganisms employed, and the generation of organic acids that contribute to alterations in the volatile and aroma profiles of roasted coffee are implicated (da Mota et al. 2020 ). Additionally the control of process variable offered by bioreactors has recently shown to contribute to the production of coffee with higher sensory quality and reproducibility (de Carvalho Neto et al. 2018 ).

The strategic diagrams and cluster networks for each period are presented in Fig.  3 (2) and (3). The volume of the spheres is proportional to the number of published documents associated with each theme. The upper-right quadrant is motor-themes, with terms in the upper-left quadrant being highly development and isolated themes. The lower-left quadrant is emerging or declining themes, while the lower-right quadrant is transversal and general. In the first period, “beverages”, “metabolomics”, and “fungal fermentation” are motor themes, while “types of fermentation” is an emergent theme. In the second period, “types of fermentation” remains an emergent theme, with “yeast” added to this category. In the third period, “coffee” is less frequent, with more specific topics such as “bacillus”, “genetics”, and “classification” as motor themes (Elhalis et al. 2021 ). For the period 2020–2022, “volatiles” and “metabolomics” are motor themes, related to research on volatiles and metobolites generated in process fermentation (Elhalis et al. 2021 ; Prakash et al. 2022 ). “Types of fermentation” and “coffee” are tranversal themes, while “lactic acid fermentation” is an emergent theme. “Bioreactors and process variables” is an isolated theme for this period.

Figure  3 (3) displays clusters of terms related to bioreactors and process variables control. The volume of spheres is proportional to the number of documents corresponding to each keyword, and the thickness of the link between two spheres is proportional to the equivalence index between these words. For the period 2001–2017, “bioreactor and process variables” is slightly related to “microorganisms”, “drying process”, “plant seed”, and “mucilage”. For the second period, “volatile” term shows a slight relationship with “bioreactor and process variables”, which in turn is associated with “coffee beans”. The main associations with “bioreactor and process variables” may be with “microorganisms” and “volatile”.

As regards the period 2021–2022 (Figs.  3 - (3) -C), strong bonds are observed between “Bioreactor and process variables”, “Food supply” and “Agriculture”, since the fermentation process is usually on-farm process, although efforts have been made to the process control (Martinez et al. 2017 ; de Carvalho Neto et al. 2018 ). Slight associations are seen with more specific terms such as “Liquid media”, “Enzymes”, “UV-VIS-Spectrophotometry” and “Biochemical analysis”. These terms are directly related to the fermentation process and its monitoring, whereby those relationships are expected.

Coffee fermentation methodologies

Scientific publications related to coffee fermentation devices were searched in the Web of Science, Scopus, and Science Direct databases. Published patents, as well as devices developed by different companies in the sector, were also included in the review. The evolution and characteristics of the devices and their impact on the quality and sensory profile of the coffee were tabulated and summarized in tables.

Table  3 presents various methods for controlling coffee fermentation, focusing on temperature, processing time, and microorganism addition. These parameters affect the grain’s physical-chemical composition and sensory profile. Fermentation times range from 12 h to several days, with low temperatures slowing microbial kinetics and requiring several days for pH to reach 3.8. Mass transfer between mucilage and grain layers occurs mainly through diffusion, leading to more complex profiles in long-time fermentation.

Evolution of technologies for coffee fermentation

Coffee fermentation devices are containers that allow the product volume to be maintained under homogeneous conditions during the process. Fermentation can be done dry or submerged, with the latter ensuring that all grains are in contact with an equal volume of oxygen. Most producers follow this method for a more homogeneous fermentation. Initially, pulped coffee was fermented in vat-type tanks made of wood, cement, or brick, which were plastered or enameled with cement or covered with baked clay veneers. The floor was built with a slope of 6 to 8% and a width-to-height ratio of 1:1.5 to facilitate leachate drainage and product removal. The final processing time was determined based on producer experience, such as the hole and touch test, which is subjective and prone to errors.

Producers have noticed that fermentation under certain conditions can result in heterogeneous coffee products with sour and fermented flavors due to the difficulty in controlling process variables. To improve sanitary conditions, Cenicafé and other manufacturers have developed high-density polyethylene vat-type tanks, which are lightweight, easy to handle, and clean. Cenicafé in Colombia has successfully maintained a stabilized process with less washing water consumption using Ecomill ® technology in stainless steel and high-density polyethylene. These systems incorporate cylindrical fermentation tanks with inverted cone-shaped bases and 60° horizontal inclination, allowing coffee to flow out by gravity.

Widyotomo, S., and Yusi, Y. ( 2013 ) evaluated the fermentation of cherry coffee in a horizontal type fermenter with electrical resistance and agitation (Fig.  4 -4-A). Working at 50% capacity (20 kg/batch), temperatures between 20 and 40 °C and times between 6 and 18 h, the authors defined optimal operating conditions at 25 °C and 12 h of processing. In an attempt to remove the mucilage using low temperatures to reduce the consumption of washing water, Bressani et al. ( 2020 ) evaluated a cold fermenter prototype. Temperatures close to 2 °C managed to denature the structure of the mucilage and then it was removed mechanically (Fig.  4 -4-B). In Brazil, some private companies have developed commercial prototypes for fermentation control. The Palinialves company developed a rotating cylinder (Fig.  4 -4-C) with a galvanized sheet, steel or stainless steel structure with internal blades and rpm control for a homogeneous mix. The system is completely sealed and has a relief valve for pressure control and temperature sensors. Its maximum capacity is 10,000 L. The Campotech company with the support of Embrapa and the Instituto Federal do Sul de Minas, developed a device for the controlled fermentation of 1,250 L of cherry or pulped coffee. The device, in the form of a vertical cylinder and conical base, has a helical agitation and temperature control systems for heating or cooling the coffee mass (Fig.  4 -4-D).

( 1 ) Vat-type tank for fermentation of pulped coffee. ( 2 ) High-density polyethylene vat-type tanks for coffee fermentation. ( A ) Cenicafé ( B ) Rotoplast ® . ( 3 ) Fermentation tank in Ecomill ® Technology. ( A ) 1,000 to 1,500 kg load capacity. ( B ) 2,000 to 6,000 kg load capacity. ( 4 ) Closed systems for coffee fermentation. ( A ) Widyotomo, S., & Yusi, Y. 2013 , ( B ) Correa et al. 2014 , ( C ) Palinialves, ( D ) CampoTech – Jacu Digital

Final remarks

Colombia, with over a century of coffee production experience, has limited knowledge in developing innovative fermentation prototypes. The fermentation process for washed coffees was once considered unimportant, focusing only on removing mucilage to reduce drying time. This neglect of safety and quality has led to issues with materials like concrete, majolica, wood, and cement. Technological advances in the last decade have led to the use of safe materials like high-density polyethylene and stainless steel in fermenters. Prototype fermenters or bioreactors with variable control systems and mechanical agitation have been developed in countries like Peru, Brazil, Chile, Spain, Indonesia, and Colombia. However, these high-cost technologies remain inaccessible to most producers. The industry has developed solutions such as helical-type central agitators and rotating drums, both with high energy consumption. A strategy is being evaluated for mixing through the recirculation of leachate, which requires less energy than the entire coffee mass. However, the impact of this methodology on the process quality has not been scientifically evaluated (Widyotomo and Yusianto 2013 ).

Conclusions

A bibliometric analysis of the literature on coffee fermentation indicates a growing interest and progress in research and development of technologies to improve sensory quality, safety, efficiency, and sustainability. Improvements in fermentation tanks have been identified in terms of materials, designs, and the incorporation of accessories such as digital sensors. Innovations in fermentation methodologies and a more scientific approach by researchers in this field have also been observed.

Moreover, the analysis indicates that issues related to coffee bean fermentation are undergoing constant evolution, with Brazil emerging as a leading contributor in this field. Despite a decline in the number of published papers over the past three years, research is focused on the design of controlled fermentations and the evaluation of the influence of microorganisms and process conditions on the sensory quality and composition of coffee. Nevertheless, it is observed that prototypes designed to regulate process variables, such as agitation and temperature, are costly and may be inaccessible to small-scale producers.

Collectively, these findings indicate that the integration of innovative technologies, enhanced methodologies, and a rigorous scientific approach is transforming the coffee industry towards enhanced efficiency, safety, and sustainability, with the potential to benefit both producers and consumers globally.

Data availability

Not applicable.

Code availability

Batista da Mota MC, Batista NN, Dias DR, Schwan RF (2022) Impact of microbial self-induced anaerobiosis fermentation (SIAF) on coffee quality. Food Biosci 47. https://doi.org/10.1016/j.fbio.2022.101640

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Project financed by the Ministry of Science and Technology of Colombia (Minciencias). Project of the General System of Royalties BPIN No. 2020000100460.

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Valeria Hurtado Cortés, Jaime Daniel Bustos Vanegas & Nelson Gutiérrez Guzmán

Present address: Facultad de Ingeniería, Grupo de Investigación Agroindustria USCO, Universidad Surcolombiana, Centro Surcolombiano de Investigación en Café – CESURCAFÉ, Avenida Pastrana Borrero Carrera 1a, Neiva, 410001, Huila, Colombia

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Facultad de Ingeniería, Grupo de Investigación Agroindustria USCO, Universidad Surcolombiana, Centro Surcolombiano de Investigación en Café – CESURCAFÉ, Avenida Pastrana Borrero Carrera 1a, Neiva, 410001, Huila, Colombia

Andrés Felipe Bahamón Monje

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The writing and formatting of the article was done by Valeria Hurtado, Jaime Bustos and Andrés Bahamon, the revision and acceptance was reviewed by Jaime Bustos and Nelson Gutierrez.

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Cortés, V.H., Bahamón Monje, A.F., Bustos Vanegas, J.D. et al. Challenges in coffee fermentation technologies: bibliometric analysis and critical review. J Food Sci Technol (2024). https://doi.org/10.1007/s13197-024-06054-5

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Revised : 06 July 2024

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Published : 02 September 2024

DOI : https://doi.org/10.1007/s13197-024-06054-5

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