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Systematic Reviews: Before you begin

A guide for researchers undertaking a systematic review

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Banner image source: Pixabay 12345 licensed under a CC0 Public Domain licence 

What is a systematic review

A systematic review aims to provide a comprehensive, unbiased synthesis of many relevant studies into a single document using rigorous and transparent methods. A systematic review aims to synthesize and summarize existing knowledge in order to inform policy and practice. 

Systematic reviews:

  • Attempt to uncover "all" of the evidence relevant to a question.
  • Should be conducted by review groups with specialized skills.
  • Set out to retrieve international evidence.
  • Follow a structured research process that requires rigorous methods to ensure that the results are unbiased, reliable and meaningful to end users.
  • Have pre-determined search strategies and eligibility criteria.
  • May or may not include a meta-analysis.
    Adapted from: Aromataris E, Munn Z. Chapter 1: JBI Systematic Reviews. In: Aromataris E, Munn Z (Editors). JBI Manual for Evidence Synthesis. JBI, 2020. Available from https://synthesismanual.jbi.global..  https://doi.org/10.46658/JBIMES-20-02

Take a look at the Cornell University Library's What Type of Review is Right for you page and the the Which Review is Right for You tool designed to provide guidance for reviewers.

Before you begin

 

Systematic reviews aim to answer a single research question.

There are many mnemonics available to assist you to formulate a search strategy based on the type of review you are undertaking and the kind of question you are asking.  You may like to consider some of techniques below to help you with this process.

Mnenomic Explanation Used for...
PICO(S) Population - Intervention - Comparator - Outcome - (Study design) Reviews of effectiveness
PICo Population - Phenomena of Interest - Context Qualitative reviews
Expert opinion / Policy
PEO Population - Exposure - Outcome Aetiology and Risk
CoCoPop Condition - Context - Popuation Prevalence and Incidence
PIRD Population - Index test - Reference test - Diagnosis of interest Diagnostic test accuracy
PCC Population - Concept - Context Scoping reviews
PICOC Population - Intervention - Comparator(s) - Outcome - Context Costs / Economic evaluation
CPIMP Construct of interest - Population - Type of measurement instrument - Measurement properties Psychometric
PFO Population - Prognostic Factors - OutcomeI Prognostic
SPIDER Sample - Phenomenon of Interest - Design  - Evaluation - Research type Qualitative and mixed methods
SPICE Setting (where?) - Perspective (for whom?) - Intervention (what?) - Comparison (Compared with what? - Evaluation (with what result?) Qualitative 
ECLIPSE Expectation (improvement or information or innovation) - Client group (at whom the service is aimed?) - Location (where is the service located?) - Impact (outcomes) - Professionals (who is involved in providing/improving service?) - Service (for which service are you looking for information?) Health policy/ Management information

 

Use the above mnemonics to construct your research question and break down your search strategy. Remember that equal emphasis may not be put on each part of the mnemonic, and will largely depend on the topic of your systematic review.

Population How would I describe a patient/problem/situation similar to mine? 
Intervention Which main intervention am I considering? 
Comparison What is the main alternative?
Outcome What could this intervention accomplish, measure, improve or affect?
Study design Which study design will best answer my question?

 

Have you checked to see if there is an existing systematic review answering your research question? This will help avoid duplication and it will help you construct your search strategy by identifying what search terms and databases were used.

To locate existing systematic reviews you can try: 

It is highly recommended that you register or publish your systematic review protocol prior to undertaking the review. This:

  • limits duplication of reviews by allowing identification of topics already under review;
  • allows peer-review of protocol, and;
  • provides a base of evidence to critically analyse the review versus protocol once complete.

For systematic reviews, umbrella reviews and rapid reviews related to health sciences, PROSPERO is a highly respected international review register. For Environmental and Agricultural sciences see the Collaboration for Environmental Evidence.

Some journals like JBI Evidence Synthesis and Systematic Reviews and Environmental Evidence also provide scope to publish systematic and scoping review protocols in other subject areas.

Please note : PROSPERO does not accept scoping reviews nor has the resources to register reviews done as part of training courses. Other places to register protocols include:

OSF Open Science Framework
Research Square
Figshare
COMRADES Collaborative Approach to Meta-Analysis and Review of Animal Data from Experimental Studies

Other types of reviews

A literature review, or narrative review, is an attempt to obtain and synthesise the results and conclusions of key publications on a given topic. Literature reviews often do not answer one specific question like a systematic review does, and they usually bring together a summary of the literature in a qualitative manner. They may be a first step in determining the current state of the literature on a topic.

A literature review may be undertaken in a systematic way in order to be comprehensive, without being a systematic review. It is important to recognise the differences between the two and determine which type of review is best suited to your needs - or whether one of the other reviews detailed here is more applicable.

Literature reviews:

  • provide a (generally qualitative) summary of the relevant literature, as determined by the author.
  • do not necessarily provide an analysis of the literature or its quality.
  • usually do not include a description of the methodology of the search process.
  • refer to key journal literature without going into the grey literature.
  • don't always answer a specific research question.
  • are not protocol driven.

 

Scoping reviews are exploratory in nature and are used to systematically search the literature and map the key concepts underpinning a research area as well as to clarify working definitions, and/or the conceptual boundaries of a topic. Scoping reviews may be undertaken as a preliminary exercise prior to the conduct of a systematic review, or as a stand alone review.

Scoping reviews may:

  • Provide direction for the ensuing systematic review or reviews or to help reviewers identify and define more precise questions and suitable inclusion criteria.
  • Assist to examine emerging evidence when it is still unclear what other, more specific questions can be posed and valuably addressed.
  • Examine broad areas to identify gaps in the evidence, clarify key concepts, and report on the types of evidence that address and inform practice in a topic area.
  • Be used to map evidence in relation to time, location, source and/or origin.

Adapted from: Peters MDJ, Marnie C, Tricco AC, Pollock D, Munn Z, Alexander L, McInerney P, Godfrey CM, Khalil H. Updated methodological guidance for the conduct of scoping reviews. JBI Evidence Synthesis. 2020;18(10):2119-2126. doi:10.11124/jbies-20-0016

Further reading and guidance:

Peters MDJ, Godfrey C, McInerney P, Munn Z, Tricco AC, Khalil, H. Chapter 11: Scoping Reviews (2020 version). In: Aromataris E, Munn Z (Editors). JBI Manual for Evidence Synthesis, JBI, 2020. Available from https://synthesismanual.jbi.global.  https://doi.org/10.46658/JBIMES-20-12

Campbell Collaboration Meta Evidence blog - Scoping Reviews

Munn Z, Peters MDJ, Stern C, Tufanaru C, McArthur A, Aromataris E. Systematic review or scoping review? Guidance for authors when choosing between a systematic or scopus review approach. BMC Med Res Methodol. 2018;18:143.

Rapid reviews are a form of accelerated systematic review. They are usually undertaken when decision makers have urgent and emerging needs which require evidence produced on a short time frame. Typically, to compensate for the short time frame of a rapid review, methodological rigour may be sacrificed. For example, the grey literature may not be sought and preference may be given to the more readily available research published and written in English. 

Adapted from: Rapid reviews. HLWIKI International. 2017. 

Umbrella reviews are sometimes referred to as a "review of reviews". They are an attempt to identify and appraise, extract and summarise all the evidence from research syntheses related to a topic or question. 

Umbrella reviews may:

  • Include analyses of different interventions for the same problem or condition.
  • Analyse the same intervention and condition, but different outcomes.
  • Analyse the same intervention but different conditions, problems or populations.

Umbrella reviews offer the possibility to address a broad scope of issues related to the topic of interest.

Adapted from: Aromataris E, Fernandez R, Godfrey C, Holly C, Khalil H, Tungpunkom P. Chapter 10: Umbrella Reviews. In: Aromataris E, Munn Z (Editors). JBI Manual for Evidence Synthesis. JBI, 2020. Available from https://synthesismanual.jbi.global.  https://doi.org/10.46658/JBIMES-20-11