Systematic Reviews: Overview

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The elements of a Systematic Review

What are the different elements of a systematic review

What is it?

A systematic review attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question. Researchers conducting systematic reviews use explicit and reproducible methods aimed at minimizing bias in the review process, in order to produce more reliable findings that can be used to inform decision making.

Reasons for choosing

To address a clearly focused review question by finding the best available, relevant research studies and synthesizing the results.

Question

Focused on a single topic.

Sources / Search

A peer review protocol or plan is included. Clear objectives are identified. Comprehensive sources and explicit and reproducible search strategy.

Eligibility criteria

Eligibility criteria is clearly defined at the outset i.e. before the review is conducted.

Selection

Criterion-based selection that is uniformly applied, clear and explicit.

Appraisal

Rigorous critical appraisal, and evaluation of study quality.

Synthesis

Clear summaries of studies based on high quality evidence.

Inferences

Evidence based.

Meta-analysis describes a statistical process for amalgamating the data from different primary studies that have investigated the same issue. All studies included in a meta-analysis should be homogenous in terms of population, intervention and outcomes. A meta-analysis provides a statistical conclusion that has a higher power than individual study results.

Part of the process when reviewing a meta-analysis is to identify the incorporation criteria (i.e. how were the studies chosen for inclusion in  the meta-analysis). Meta-analysis most commonly follows a systematic review of the literature but it does not have to (i.e. you can do a meta-analysis without doing a systemic review). However, the rigour of the meta-analysis will be affected if there is no systematic searching and critical appraisal of the literature.

Watch the following by Dr Saravana Kumar (Senior Lecturer in Physiotherapy, UniSA).

Type Overview
Narrative (literature) review Synthesizes the findings of literature retrieved from searches of computerised databases, hand searches, and authoritative texts.
Critical review Shows that the literature has been extensively researched and critically evaluated. Goes beyond the narrative review as it contains a degree of analysis and conceptual innovation of the literature.
Scoping review Rapid gathering of literature in a given policy or clinical area where the aims are to accumulate as much evidence as possible and map the results and provide an overview of the type, extent and quantity of research available on a given topic.
Rapid review Uses systematic review methods to search and critically appraise the literature to assess what is already known about a particular policy or issue. How complete the searches are depends on time factors.
Systematic review Attempts to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question. Researchers conducting systematic reviews use explicit and reproducible methods aimed at minimizing bias in the review process, in order to produce more reliable findings that can be used to inform decision making.
Umbrella review Focuses on a broad condition or problem and compiles evidence from other reviews into one document which highlights competing interventions. Does not include primary studies.

Adapted from: 'A typology of reviews' (pp.94-5).

Not sure if this is the review type for you?

Please visit library's guides for other review types

The systematic review in context:

Review types [Image source: HLWIKI International, http://hlwiki.slais.ubc.ca/index.php/File:Evidence-review-types.jpg, copied under: CC BY-NC-SA 2.5 CA, https://creativecommons.org/licenses/by-nc-sa/2.5/ca/]

Source: HLWIKI International, copied under Creative Commons (CC BY-NC-SA 2.5 CA)

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Guidelines and standards

Using a standard or guidelines will help you conduct your systematic review. 

Cochrane Library logo [Image source: Cochrane Library, http://www.cochranelibrary.com/] Campbell Collaboration logo [Copied from: https://www.campbellcollaboration.org/] Finding what works in health care [Image source: The National Academies Press, https://www.nap.edu/catalog/13059/finding-what-works-in-health-care-standards-for-systematic-reviews]

Cochrane Library logo [Image source: Cochrane Library, http://www.cochranelibrary.com/]

Campbell Collaboration logo [Copied from: https://www.campbellcollaboration.org/]

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Image attributions

The process

Step 1 - A clear and focused question.

  • This may require preliminary searching (scoping) to see what evidence is already available and whether a Systematic Reviews has been done before.

Step 2 - Develop a protocol.

  • This is your plan (or recipe) for your review.
    • Search strategy and databases
    • Eligibility criteria
    • Screening process
    • Critical appraisal process
    • Data analysis / synthesis process
  • Register your protocol with Prospero or publish it in a relevant journal.

 

Then, per your protocol:

Step 3 - Conduct systematic searches.

Step 4 - Screen results for relevant studies that meet your eligibility criteria.

Step 5 - Pearling (optional)

  • This is the step where the reference lists of relevant articles are examined for articles that may have been missed by the database searches. The references selected are then screened.

Step 6 - Critically appraise the quality of the included studies.

Step 7 - Extract relevant data from the included studies.

Step 8 - Data synthesis.

Step 9 - Summarise and interpret the evidence to answer your question.

Further resources