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Systematic Reviews

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

Systematic review - Definition

A systematic review is a type of secondary evidence that summarises research that has already been published.

As defined by the Cochrane Collaboration a systematic review is:

"A review of a clearly formulated question that uses systematic and explicit methods to identify, select, and critically appraise relevant research, and to collect and analyse data from the studies that are included in the review. Statistical methods (meta-analysis) may or may not be used to analyse and summarise the results of the included studies."


 

What are Systematic Reviews? (3:23 min) by Cochrane (YouTube)

Evidence based practice

When conducting a systematic review it is important to ask a question that can be answered through use of evidence, rather than subjective judgment. In evidence based practice, systematic reviews are considered one of the highest levels of information.

Image: What's In a Name?: the Difference Between a Systematic Review and a Literature Review and Why It Matters by Lynn Kysh / CC-BY 4.0


A systematic review may sometimes include a meta-analysis. A meta-analysis is the use of statistical methods to combine data from studies included in a systematic review. Not all systematic reviews include a meta-analysis.

Image: What's In a Name?: the Difference Between a Systematic Review and a Literature Review and Why It Matters by Lynn Kysh / CC-BY 4.0

Systematic review vs. Literature review

A systematic review is a type of literature review. The differences between a systematic review and a literature review are outlined in the following table.

Image: What's In a Name?: the Difference Between a Systematic Review and a Literature Review and Why It Matters by Lynn Kysh / CC-BY 4.0

Types of reviews

An overview of different types of reviews is provided in the following paper. The table is an adaptation from the paper.

 

  Literature reviews Systematic reviews Meta-analysis Scoping review Rapid review

Description

Generic term: published materials that provide an examination of recent or current literature. It can cover a wide range of subjects at various levels of completeness and comprehensiveness. May include research findings.

Seeks to systematically search for, appraise, and synthesise research evidence, often adhering to guidelines on the conduct of a review.

Technique that statistically combines the results of quantitative studies to provide a more precise effect of the results.

Preliminary assessment of potential size and scope of available research literature. Aims to identify the nature and extent of research evidence (usually including ongoing research).

Assessment of what is already known about a policy or practice issue, by using systematic review methods to search and critically appraise existing research.

Search May, or may not, include comprehensive searching. Aims for exhaustive, comprehensive searching. Aims for exhaustive, comprehensive searching. May use a funnel plot to assess completeness. Completeness of searching determined by time/scope constraints. May include research in progress. Completeness of searching determined by time constraints.
Appraisal May, or may not, include quality assessment. Quality assessment may determine inclusion/exclusion. Quality assessment may determine inclusion/exclusion and/or sensitivity analyses. No formal quality assessment. Time‐limited formal quality assessment.
Synthesis Typically narrative. Typically narrative with tabular accompaniment. Graphical and tabular with narrative commentary. Typically tabular with some narrative commentary. Typically narrative and tabular.
Analysis Analysis may be chronological, conceptual, thematic, etc. What is known; recommendations for practice. What remains unknown; uncertainty around findings, recommendations for future research. Numerical analysis of measures of effect assuming the absence of heterogeneity. Characterises quantity and quality of literature, perhaps by study design and other key features. Attempts to specify a viable review. Quantities of literature and overall quality/direction of effect of literature.

Further reading: