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Clerkship Resources: Systematic Reviews and Meta-Analyses

Keys to success in the clerkships and beyond.

Evidence Syntheses: Systematic Reviews and Meta-Analysis

Most experts consider well done systematic reviews, with or without meta-analysis, to provide the best evidence for all question types. The major advantage of systematic reviews is that they are based on the findings of multiple studies that were identified in comprehensive, systematic literature searches. 

The position of systematic reviews at the top of the evidence hierarchy is not absolute, however. 

  • You must appraise a systematic review's methodological rigor and the strength of its findings before applying those findings to patient care.
  • Systematic reviews often take months to years to conduct. Make sure that the findings of a systematic review have not been superseded by newer evidence.
  • A large, well conducted randomized controlled trial may provide more compelling evidence than a systematic review of small, underpowered trials.

Systematic Reviews vs. Narrative Reviews

Beginning EBM practitioners often have difficulty distinguishing between the evidence and the evidence-based literature. MEDLINE adds to the confusion because it classifies both systematic reviews of the literature and the more common narrative reviews as Review [Publication Type].

Systematic reviews seek to answer clearly formulated questions by using rigorous, explicit protocols to identify, select and appraise relevant research studies; and to collect and analyze data from the selected studies. To minimize bias, systematic reviews include or exclude evidence on the basis of explicit quality criteria.They may incorporate meta-analysis.

Narrative reviews articles may be evidence-based, but they are NOT evidence (research). They usually lack systematic search protocols or explicit criteria for selecting and appraising evidence. Instead, they rely on experts to gather evidence and synthesize findings. 

Systematic Reviews
Narrative Reviews
Investigate a clearly defined topic or question. Intended to provide an overview of an area.
Literature is gathered using explicit search protocols. Explicit, systematic literature search protocol not used.
Studies selected for the review using a protocol that specifies inclusion, exclusion criteria. Studies used to support the reviewers' recommendations are not selected according to an explicit, predetermined protocol.
Data from primary study may be synthesized in a meta-analysis. Evidence "grades" may be applied to individual studies. May use a level of evidence rating system to "grade" the quality and strength of individual studies.
When evidence is lacking, the authors usually recommend further research. When evidence is lacking, the authors make recommendations based on their opinions and experience. Recommendations may be "graded" based on the consistency and strength of the underlying evidence.