Appraising Systematic Reviews and Meta-analyses

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Abstract
A systematic review is an overview that answers a specific clinical question and contains a thorough, unbiased search of the relevant literature, explicit criteria for assessing studies, and a structured presentation of the results. Many systematic reviews incorporate a meta-analysis, ie, a quantitative pooling of several similar studies to produce an overall summary of treatment effect.1,2 Meta-analysis provides an objective and quantitative summary of evidence that is amenable to statistical analysis,1 and it allows recognition of important treatment effects by combining the results of small trials that individually might have lacked the power to consistently demonstrate differences among treatments. Meta-analysis has been criticized for the discrepancies between its findings and those of large clinical trials.3- 6 The frequency of discrepancies ranges from 10% to 23%3 and can often be explained by differences in treatment protocols or study populations or changes that occur over time.3