Meta-analyses and Systematic Reviews
Systematic reviews are research summaries that address a focused clinical question in a structured, reproducible manner, often accompanied by a meta-analysis, which is a statistical pooling of results from different studies providing a single estimate of effect. When searching for evidence to answer a clinical question, it is preferable to seek a systematic review, especially one that includes a meta-analysis. Single studies are liable to be unrepresentative of the total evidence and be misleading. Systematic reviews include a greater range of patients than any single study, potentially enhancing confidence in applying the results to the patient at hand.
When clinicians apply the results of a systematic review or meta-analysis to patient care, they should start by evaluating the credibility of the methods of the systematic review. Credibility depends on whether the review addressed a sensible clinical question; included an exhaustive literature search; demonstrated reproducibility of the selection and assessment of studies; and presented results in a useful manner.
For reviews that are sufficiently credible, clinicians must decide on the degree of confidence in the estimates that the evidence warrants (quality of evidence). Confidence depends on the risk of bias in the body of evidence; the precision and consistency of the results; whether the results directly apply to the patient of interest; and the likelihood of reporting bias. Shared decision making requires understanding of the estimates of magnitude of beneficial and harmful effects, and confidence in those estimates.
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