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Systematic Reviews and Evidence Synthesis

Systematic Reviews and other types of evidence synthesis

Evidence synthesis decision tree

Evidence synthesis refers to any method of identifying, selecting, and combining results from multiple studies. For help selecting a methodology, consult the Review Methodology Decision Tree developed by Cornell University.

Types of evidence synthesis

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 typically takes 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.
  • Maybe conducted independently or as part of a systematic review.