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Systematic Reviews

This guide introduces the process of conducting a systematic review of the literature.

What to include

In general, the writing process for a systematic review is similar to the process of writing any other kind of review.

A systematic review should provide an answer to the research question, it is not a broad overview of current trends and gaps in research. The review should show the reader how the answer was found, and provide the results you have identified.

A systematic review must have a detailed methodology that describes the search process and the selection process. This is why careful documentation of the methodology is important. A reader of the review should be able to critically interpret the findings- to understand why sources were chosen, how they were assessed, and how conclusions were reached.

The structure of the systematic review differs from the narrative review or the traditional literature review that allows you to organise it to best support your argument. A systematic review should reflect the stages outlined in the protocol. With a systematic review reporting guidelines should be followed that help you identify what should be included in each section of the review. One such standard approach is PRISMA.

Although much time is invested in developing a search strategy and screening results, a systematic review is valued by the critical reflection and interpretation of the findings. Focus on analysing, not summarising. Use a critical analysis tool to assess the studies.

Your systematic review needs to tell a story, and it needs to clearly articulate how it provides meaningful and original advancement of the field.

Abstract

The abstract provides an overview of the systematic review. It usually covers the following:

  • A brief background (what we know and often the gap that the review will fill)
  • The aim or hypothesis
  • Summary of methods
  • Summary of results
  • Summary of conclusion (and sometimes recommendations).

Note that these points represent the general ‘story line’ seen in most systematic reviews: What we know (and perhaps what the gap is); what we set out to do; what we did; what we found; what this means.

Introduction

The introduction provides an overview of the systematic review and enough contextual information for the reader to make sense of the remainder of the report. It usually covers the following:

  • Background information to contextualise the review (what we already know about this area)
  • Definitions of key terms and concepts if needed
  • The rationale for the study (often in terms of a gap in knowledge that needs to be filled, a lack of agreement within the literature that needs to be resolved, or the potential implications of the findings)
  • The aims and/or objectives (optional)
  • The research question/s emanating from the rationale
  • Additional information (Optional)

Note however, that these points are not always in this order. Some writers prefer to begin with the research questions, followed by the context, building to the rationale.

Methods

The methods section can be divided up into two main sections.

The first section describes how the literature search was conducted. This section may contain any of the following information: 

  • The databases searched and whether any manual searches were completed 
  • How search terms were identified 
  • What terms were employed in the key word searches 
  • If particular sections of articles were looked at during the search and collection stage i.e. titles, abstracts, table of contents (note: the information in these sections may have informed the selection process) 

The second section discusses the criteria for including or excluding studies. This section may include any of the following information:

  • Your selection criteria
  • How you identified relevant studies for further analysis 
  • What articles you reviewed 
  • What particular areas you looked at in the selected articles i.e. a relationship or association between two things (such as a genetic predisposition and a drug), the outcome measures of a health campaign, drug treatment, or clinical intervention, the differing impact of a particular drug or treatment. 

Details about the kind of systematic review undertaken, i.e. thematic analysis, might also be mentioned in the methods section.​

Results

Broadly speaking, in the results section, everything you have done so far needs to be presented.  This can include any of the following: ​

  • Number of studies screened, assessed for eligibility and included in the review, with reasons for exclusion at each stage. This may mean you need to:
    • briefly mention the databases used for the searching
    • identify the number of hits
    • show how the articles were selected by title, abstract, table of contents or other procedures. 
  • Overview of the kinds of studies selected for the review i.e. the types of methodologies or study designs used.
  • Basic characteristics of the included studies. This may involve discussing: 
    • where the trials were conducted
    • treatment duration
    • details about participants
    • similarities and differences in the way data was measured
    • similar or different approaches to the same treatment or condition 
  • Risk of bias across studies 
  • Results of individual studies. This can include:
    • the kinds of relationships or associations demonstrated by the studies
    • frequency of positive or adverse effects of a particular treatment or drug
    • the number of studies that found a positive correlation between two phenomena or found a causal relationship between two variables

Often, researchers will include tables in the Results section or Appendix to provide on overview of data found in the studies. Remember, tables in the Results section need to be explained fully.

Discussion and Conclusion

A primary function of your discussion and conclusion is to help readers understand the main findings and implications of the review.

The following elements are commonly found in the discussion and conclusion sections. Note that the points listed are neither mandatory nor in any prescribed order.   

Discussion:

  • Summary of main findings
  • Interpretation of main findings (don’t repeat results)
  • Strengths and weaknesses
  • Comparison with previous review findings or general literature
  • The degree to which the review answers the research question
  • Whether the hypothesis was confirmed
  • Limitations (e.g. biases, lack of methodological rigour or weak evidence in the articles)

Conclusion:

  • Summary of how it answers the research question (the ‘take home’ message)
  • Significance of the findings
  • Reminder of the limitations
  • Implications and recommendations for further research.

Separate or combined?

A key difference between a discussion and a conclusion relates to how specific or general the observations are. A discussion closely interprets results in the context of the review. A conclusion identifies the significance and the implications beyond the review. Some reviews present these as separately headed sections. Many reviews, however, present only one section using a combination of elements. This section may be headed either Discussion or Conclusion.