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What is a literature review?

A literature review is an integrated analysis -- not just a summary-- of scholarly writings and other relevant evidence related directly to your research question.  That is, it represents a synthesis of the evidence that provides background information on your topic and shows a association between the evidence and your research question.

A literature review may be a stand alone work or the introduction to a larger research paper, depending on the assignment.  Rely heavily on the guidelines your instructor has given you.

Why is it important?

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Discovers relationships between research studies/ideas.
• Identifies major themes, concepts, and researchers on a topic.
• Identifies critical gaps and points of disagreement.
• Discusses further research questions that logically come out of the previous studies.

APA7 Style resources

APA Style Blog - for those harder to find answers

1. Choose a topic. Define your research question.

Your literature review should be guided by your central research question.  The literature represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.

• Make sure your research question is not too broad or too narrow.  Is it manageable?
• Begin writing down terms that are related to your question. These will be useful for searches later.
• If you have the opportunity, discuss your topic with your professor and your class mates.

2. Decide on the scope of your review

How many studies do you need to look at? How comprehensive should it be? How many years should it cover? 

• This may depend on your assignment.  How many sources does the assignment require?

3. Select the databases you will use to conduct your searches.

Make a list of the databases you will search. 

Where to find databases:

• use the tabs on this guide
• Find other databases in the Nursing Information Resources web page
• More on the Medical Library web page
• ... and more on the Yale University Library web page

4. Conduct your searches to find the evidence. Keep track of your searches.

• Use the key words in your question, as well as synonyms for those words, as terms in your search. Use the database tutorials for help.
• Save the searches in the databases. This saves time when you want to redo, or modify, the searches. It is also helpful to use as a guide is the searches are not finding any useful results.
• Review the abstracts of research studies carefully. This will save you time.
• Use the bibliographies and references of research studies you find to locate others.
• Check with your professor, or a subject expert in the field, if you are missing any key works in the field.
• Ask your librarian for help at any time.
• Use a citation manager, such as EndNote as the repository for your citations. See the EndNote tutorials for help.

Review the literature

Some questions to help you analyze the research:

• What was the research question of the study you are reviewing? What were the authors trying to discover?
• Was the research funded by a source that could influence the findings?
• What were the research methodologies? Analyze its literature review, the samples and variables used, the results, and the conclusions.
• Does the research seem to be complete? Could it have been conducted more soundly? What further questions does it raise?
• If there are conflicting studies, why do you think that is?
• How are the authors viewed in the field? Has this study been cited? If so, how has it been analyzed?

Tips: 

• Review the abstracts carefully.  
• Keep careful notes so that you may track your thought processes during the research process.
• Create a matrix of the studies for easy analysis, and synthesis, across all of the studies.
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Coeytaux RR, McDuffie J, Goode A, et al. Evidence Map of Yoga for High-Impact Conditions Affecting Veterans [Internet]. Washington (DC): Department of Veterans Affairs (US); 2014 Aug.

Evidence Map of Yoga for High-Impact Conditions Affecting Veterans [Internet].

Appendix d criteria used in quality assessment of systematic reviews.

For reviews, first determine whether it is a systematic review. To be a systematic review, it must include a methods section that describes (1) a search strategy and (2) an a priori approach to synthesizing the data. For reviews determined to meet the systematic review criteria, assess methodological quality, following the instructions below.

General instructions: The purpose of this rating tool is to evaluate the scientific quality of systematic reviews. It is not intended to measure the literary quality, importance, relevance, originality, or other attributes of systematic reviews.

Step 1: Grade each criterion listed below as “Yes,” “No,” “Can't tell” or “Not Applicable” (N/A). Factors to consider when making an assessment are listed under each criterion. Where appropriate (particularly when assigning a “No” or “Can't tell” score), please provide a brief rationale for your decision (in parentheses).

• Is a focused clinical question clearly stated? At a minimum, the question should be developed a priori and should clearly identify population and outcomes. The study question does not have to be in PICO format (Population, Intervention, Comparisons, Outcomes). [] Yes [] No [] Can't tell [] N/A
• Are the search methods used to identify relevant studies clearly described? Search methods described in enough detail to permit replication. (The report must include search date, databases used, and search terms. Keywords and/or MeSH terms must be stated and where feasible the search strategy should be provided.) [] Yes [] No [] Can't tell [] N/A
• Was a comprehensive literature search performed? At least 2 electronic sources should be searched and electronic searches should be supplemented by consulting: reference lists from prior reviews, textbooks, or included studies; specialized registries (eg, Cochrane registries); or queries to experts in the field. [] Yes [] No [] Can't tell [] N/A
• Was selection bias avoided? Study reports the number of studies identified through searches, the numbers excluded, and gives appropriate reasons for excluding, based on explicit inclusion/exclusion criteria. [] Yes [] No [] Can't tell [] N/A
• Was there duplicate study selection and data extraction? Did two or more raters make inclusion/exclusion decisions, abstract data, and assess study quality – either independently or with one rater over-reading the first raters result? Was an appropriate method used to resolve disagreements (eg, a consensus procedure)? [] Yes [] No [] Can't tell [] N/A
• Were the characteristics of the included studies provided? In an aggregated form such as a table, data from the original studies should be provided on the participants, interventions, and outcomes. The ranges of characteristics in all the studies analyzed (eg, age, race, sex, relevant socioeconomic data, disease status, duration, severity or other diseases) should be reported. [] Yes [] No [] Can't tell [] N/A
• Was the scientific quality of the included studies assessed and documented? A priori methods of assessment should be provided and criteria used to assess study quality specified in enough detail to permit replication. [] Yes [] No [] Can't tell [] N/A
• Were the methods used to combine the findings of studies appropriate? For pooled results, an accepted quantitative method of pooling should be used (ie, more than simple addition; eg, random-effects or fixed-effect model). For pooled results, a qualitative and quantitative assessment of homogeneity (Cochran's Q and/or I2) should be performed. If only qualitative analyses are completed, the study should describe the reasons that quantitative analyses were not completed. [] Yes [] No [] Can't tell [] N/A
• Was the scientific quality of the included studies used appropriately in formulating conclusions? The results of the methodological rigor and scientific quality should be considered in the analysis (eg, subgroup analyses) and the conclusions of the review, and explicitly stated in formulating recommendations. [] Yes [] No [] Can't tell [] N/A
• Was publication bias assessed? Publication bias tested using funnel plots, test statistics (eg, Egger's regression test), and/or search of trials registry for unpublished studies. [] Yes [] No [] Can't tell [] N/A
• Was the conflict of interest stated? Potential sources of support should be clearly acknowledged in both the systematic review and the included studies. [] Yes [] No [] Can't tell [] N/A
• Are the stated conclusions supported by the data presented? Were the conclusions made by the author(s) supported by the data and/or analyses reported in the systematic review? [] Yes [] No [] Can't tell [] N/A
• Cite this Page Coeytaux RR, McDuffie J, Goode A, et al. Evidence Map of Yoga for High-Impact Conditions Affecting Veterans [Internet]. Washington (DC): Department of Veterans Affairs (US); 2014 Aug. APPENDIX D, Criteria Used in Quality Assessment of Systematic Reviews.
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7 Writing a Literature Review

Hundreds of original investigation research articles on health science topics are published each year. It is becoming harder and harder to keep on top of all new findings in a topic area and – more importantly – to work out how they all fit together to determine our current understanding of a topic. This is where literature reviews come in.

In this chapter, we explain what a literature review is and outline the stages involved in writing one. We also provide practical tips on how to communicate the results of a review of current literature on a topic in the format of a literature review.

7.1 What is a literature review?

Literature reviews provide a synthesis and evaluation  of the existing literature on a particular topic with the aim of gaining a new, deeper understanding of the topic.

Published literature reviews are typically written by scientists who are experts in that particular area of science. Usually, they will be widely published as authors of their own original work, making them highly qualified to author a literature review.

However, literature reviews are still subject to peer review before being published. Literature reviews provide an important bridge between the expert scientific community and many other communities, such as science journalists, teachers, and medical and allied health professionals. When the most up-to-date knowledge reaches such audiences, it is more likely that this information will find its way to the general public. When this happens, – the ultimate good of science can be realised.

A literature review is structured differently from an original research article. It is developed based on themes, rather than stages of the scientific method.

In the article Ten simple rules for writing a literature review , Marco Pautasso explains the importance of literature reviews:

Literature reviews are in great demand in most scientific fields. Their need stems from the ever-increasing output of scientific publications. For example, compared to 1991, in 2008 three, eight, and forty times more papers were indexed in Web of Science on malaria, obesity, and biodiversity, respectively. Given such mountains of papers, scientists cannot be expected to examine in detail every single new paper relevant to their interests. Thus, it is both advantageous and necessary to rely on regular summaries of the recent literature. Although recognition for scientists mainly comes from primary research, timely literature reviews can lead to new synthetic insights and are often widely read. For such summaries to be useful, however, they need to be compiled in a professional way (Pautasso, 2013, para. 1).

An example of a literature review is shown in Figure 7.1.

Video 7.1: What is a literature review? [2 mins, 11 secs]

Watch this video created by Steely Library at Northern Kentucky Library called ‘ What is a literature review? Note: Closed captions are available by clicking on the CC button below.

Examples of published literature reviews

• Strength training alone, exercise therapy alone, and exercise therapy with passive manual mobilisation each reduce pain and disability in people with knee osteoarthritis: a systematic review
• Traveler’s diarrhea: a clinical review
• Cultural concepts of distress and psychiatric disorders: literature review and research recommendations for global mental health epidemiology

7.2 Steps of writing a literature review

Writing a literature review is a very challenging task. Figure 7.2 summarises the steps of writing a literature review. Depending on why you are writing your literature review, you may be given a topic area, or may choose a topic that particularly interests you or is related to a research project that you wish to undertake.

Chapter 6 provides instructions on finding scientific literature that would form the basis for your literature review.

Once you have your topic and have accessed the literature, the next stages (analysis, synthesis and evaluation) are challenging. Next, we look at these important cognitive skills student scientists will need to develop and employ to successfully write a literature review, and provide some guidance for navigating these stages.

Analysis, synthesis and evaluation

Analysis, synthesis and evaluation are three essential skills required by scientists  and you will need to develop these skills if you are to write a good literature review ( Figure 7.3 ). These important cognitive skills are discussed in more detail in Chapter 9.

The first step in writing a literature review is to analyse the original investigation research papers that you have gathered related to your topic.

Analysis requires examining the papers methodically and in detail, so you can understand and interpret aspects of the study described in each research article.

An analysis grid is a simple tool you can use to help with the careful examination and breakdown of each paper. This tool will allow you to create a concise summary of each research paper; see Table 7.1 for an example of  an analysis grid. When filling in the grid, the aim is to draw out key aspects of each research paper. Use a different row for each paper, and a different column for each aspect of the paper ( Tables 7.2 and 7.3 show how completed analysis grid may look).

Before completing your own grid, look at these examples and note the types of information that have been included, as well as the level of detail. Completing an analysis grid with a sufficient level of detail will help you to complete the synthesis and evaluation stages effectively. This grid will allow you to more easily observe similarities and differences across the findings of the research papers and to identify possible explanations (e.g., differences in methodologies employed) for observed differences between the findings of different research papers.

Table 7.1: Example of an analysis grid

Table 7.3: Sample filled-in analysis grid for research article by Ping and colleagues

Source: Ping, WC, Keong, CC & Bandyopadhyay, A 2010, ‘Effects of acute supplementation of caffeine on cardiorespiratory responses during endurance running in a hot and humid climate’, Indian Journal of Medical Research, vol. 132, pp. 36–41. Used under a CC-BY-NC-SA licence.

Step two of writing a literature review is synthesis.

Synthesis describes combining separate components or elements to form a connected whole.

You will use the results of your analysis to find themes to build your literature review around. Each of the themes identified will become a subheading within the body of your literature review.

A good place to start when identifying themes is with the dependent variables (results/findings) that were investigated in the research studies.

Because all of the research articles you are incorporating into your literature review are related to your topic, it is likely that they have similar study designs and have measured similar dependent variables. Review the ‘Results’ column of your analysis grid. You may like to collate the common themes in a synthesis grid (see, for example Table 7.4 ).

Step three of writing a literature review is evaluation, which can only be done after carefully analysing your research papers and synthesising the common themes (findings).

During the evaluation stage, you are making judgements on the themes presented in the research articles that you have read. This includes providing physiological explanations for the findings. It may be useful to refer to the discussion section of published original investigation research papers, or another literature review, where the authors may mention tested or hypothetical physiological mechanisms that may explain their findings.

When the findings of the investigations related to a particular theme are inconsistent (e.g., one study shows that caffeine effects performance and another study shows that caffeine had no effect on performance) you should attempt to provide explanations of why the results differ, including physiological explanations. A good place to start is by comparing the methodologies to determine if there are any differences that may explain the differences in the findings (see the ‘Experimental design’ column of your analysis grid). An example of evaluation is shown in the examples that follow in this section, under ‘Running performance’ and ‘RPE ratings’.

When the findings of the papers related to a particular theme are consistent (e.g., caffeine had no effect on oxygen uptake in both studies) an evaluation should include an explanation of why the results are similar. Once again, include physiological explanations. It is still a good idea to compare methodologies as a background to the evaluation. An example of evaluation is shown in the following under ‘Oxygen consumption’.

7.3 Writing your literature review

Once you have completed the analysis, and synthesis grids and written your evaluation of the research papers , you can combine synthesis and evaluation information to create a paragraph for a literature review ( Figure 7.4 ).

The following paragraphs are an example of combining the outcome of the synthesis and evaluation stages to produce a paragraph for a literature review.

Note that this is an example using only two papers – most literature reviews would be presenting information on many more papers than this ( (e.g., 106 papers in the review article by Bain and colleagues discussed later in this chapter). However, the same principle applies regardless of the number of papers reviewed.

The next part of this chapter looks at the each section of a literature review and explains how to write them by referring to a review article that was published in Frontiers in Physiology and shown in Figure 7.1. Each section from the published article is annotated to highlight important features of the format of the review article, and identifies the synthesis and evaluation information.

In the examination of each review article section we will point out examples of how the authors have presented certain information and where they display application of important cognitive processes; we will use the colour code shown below:

This should be one paragraph that accurately reflects the contents of the review article.

Introduction

The introduction should establish the context and importance of the review

Body of literature review

The reference section provides a list of the references that you cited in the body of your review article. The format will depend on the journal of publication as each journal has their own specific referencing format.

It is important to accurately cite references in research papers to acknowledge your sources and ensure credit is appropriately given to authors of work you have referred to. An accurate and comprehensive reference list also shows your readers that you are well-read in your topic area and are aware of the key papers that provide the context to your research.

It is important to keep track of your resources and to reference them consistently in the format required by the publication in which your work will appear. Most scientists will use reference management software to store details of all of the journal articles (and other sources) they use while writing their review article. This software also automates the process of adding in-text references and creating a reference list. In the review article by Bain et al. (2014) used as an example in this chapter, the reference list contains 106 items, so you can imagine how much help referencing software would be. Chapter 5 shows you how to use EndNote, one example of reference management software.

Click the drop down below to review the terms learned from this chapter.

Copyright note:

• The quotation from Pautasso, M 2013, ‘Ten simple rules for writing a literature review’, PLoS Computational Biology is use under a CC-BY licence. 
• Content from the annotated article and tables are based on Schubert, MM, Astorino, TA & Azevedo, JJL 2013, ‘The effects of caffeinated ‘energy shots’ on time trial performance’, Nutrients, vol. 5, no. 6, pp. 2062–2075 (used under a CC-BY 3.0 licence ) and P ing, WC, Keong , CC & Bandyopadhyay, A 2010, ‘Effects of acute supplementation of caffeine on cardiorespiratory responses during endurance running in a hot and humid climate’, Indian Journal of Medical Research, vol. 132, pp. 36–41 (used under a CC-BY-NC-SA 4.0 licence ). 

Bain, A.R., Morrison, S.A., & Ainslie, P.N. (2014). Cerebral oxygenation and hyperthermia. Frontiers in Physiology, 5 , 92.

Pautasso, M. (2013). Ten simple rules for writing a literature review. PLoS Computational Biology, 9 (7), e1003149.

How To Do Science Copyright © 2022 by University of Southern Queensland is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Health Sciences Writing

• Writing Resources
• Annotated Bibliography

Literature Review

• Grant or Research Proposals
• Assessing Sources

These resources can help you conduct a literature review:

• Cleveland Health Sciences Library
• Systematic Review Guide
• Link to the library's health sciences databases   (CINAHL, Scopus, Web of Science)

The literature review assignment is designed to help you situate a potential specific research question, and your answer to that question, within a well-delineated body of academic research. For an in-depth discussion of literature reviews, please review our  Systematic Review Guide.

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Literature Reviews (Health Sciences)

• What is a Literature Review?
• Best Practices
• Research Question Development
• Written Protocol
• Inclusion/Exclusion Criteria
• Librarian Collaboration
• Search Documentation
• Screening Results

Quality Assessment

Quality assessment (by study design).

• Reference Management

Once screening (article selection) is completed, the Quality Assessment part of the systematic review process may begin. Quality assessment may be performed before data extraction, or after.

Since systematic reviews rely on data from other studies, the evidence in a systematic review is only as good as, or as free from bias as, the included studies. Therefore, the methodological quality of each individual study included in a systematic review should be assessed. This process involves appraising, judging, and documenting potential risks of bias.

The quality assessment tool is based upon the types of studies which will be included in your systematic review.

We recommend that you use Covidence to conduct quality assessment.

• Covidence: help guide (quality assessment)
• Risk of Bias / Quality Assessment Tools
• Randomized Controlled Trials
• Cohort Studies
• Case-Control Studies
• Other Study Designs

For help in deciding which risk of bias / quality assessment tool(s) to use, consult one of the following sites:

• LATITUDES Network
• OSF Quality Assessment and Risk of Bias Tool Repository : download the spreadsheet named, "Repository of Quality Assessment and Risk of Bias Tools OSF" and use the  Study Type/Intended Use  dropdown menu in column F to find recommended tools based on study design.
• NIH Office of Management  quality assessment tools  
• Cochrane Risk of Bias (ROB) 2.0 Tool Templates are tailored to randomized parallel-group trials, cluster-randomized parallel-group trails (including stepped-wedge designs), and randomized cross-over trails and other matched designs.
• CASP- Randomized Controlled Trial Appraisal Tool A checklist for RCTs created by the Critical Appraisal Skills Program (CASP)
• Checklist for Randomized Controlled Trials (JBI) A critical appraisal checklist from the Joanna Briggs Institute (JBI)
• The Newcastle-Ottawa Scale (NOS) for assessing the quality of nonrandomised studies in meta-analyses Validated tool for assessing case-control and cohort studies.
• CASP- Cohort Studies A checklist created by the Critical Appraisal Skills Programme (CASP) to assess key criteria relevant to cohort studies.
• Checklist for Cohort Studies (JBI) A checklist for cohort studies from the Joanna Briggs Institute.
• STROBE Checklist A checklist for quality assessment of case-control, cohort, and cross-sectional studies.
• CASP- Case Control Study A checklist created by the Critical Appraisal Skills Programme (CASP) to assess key criteria relevant to case-control studies.
• Tool to Assess Risk of Bias in Case Control Studies by the CLARITY Group at McMaster University A quality assessment tool for case-control studies from the CLARITY Group at McMaster University.
• JBI Checklist for Case-Control Studies A checklist created by the Joanna Briggs Institute.
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