A Guide to Evidence Synthesis: Types of Evidence Synthesis

Types of Evidence Synthesis

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Evidence synthesis refers to any method of identifying, selecting, and combining results from multiple studies. For help selecting a methodology, try our review methodology decision tree. Types of evidence synthesis include: 

​​Systematic Review

• Systematically and transparently collect and categorize existing evidence on a broad question of scientific, policy or management importance.
• Compares, evaluates, and synthesizes evidence in a search for the effect of an intervention. 
• Time-intensive and often take months to a year or more to complete. 
• The most commonly referred to type of evidence synthesis. Sometimes confused as a blanket term for other types of reviews.

​​Literature (Narrative) Review

• A broad term referring to reviews with a wide scope and non-standardized methodology. 
• Search strategies, comprehensiveness, and time range covered will vary and do not follow an established protocol.

​Scoping Review or Evidence Map

• Systematically and transparently collect and categorize existing evidence on a broad question of scientific, policy or management importance.
• Seeks to identify research gaps and opportunities for evidence synthesis rather than searching for the effect of an intervention. 
• May critically evaluate existing evidence, but does not attempt to synthesize the results in the way a systematic review would. (see EE Journal and CIFOR)
• May take longer than a systematic review.
• See Arksey and O'Malley (2005) for methodological guidance.

​Rapid Review

• Applies Systematic Review methodology within a time-constrained setting.
• Employs methodological "shortcuts" (limiting search terms for example) at the risk of introducing bias.
• Useful for addressing issues needing quick decisions, such as developing policy recommendations.
• See Evidence Summaries: The Evolution of a Rapid Review Approach

Umbrella Review

• Reviews other systematic reviews on a topic. 
• Often defines a broader question than is typical of a traditional systematic review.
• Most useful when there are competing interventions to consider.

Meta-analysis

• Statistical technique for combining the findings from disparate quantitative studies.
• Uses statistical methods to objectively evaluate, synthesize, and summarize results.
• May be conducted independently or as part of a systematic review.