Meta-analysis: a critical appraisal of the methodology, benefits and drawbacks

Meta-analysis has become an integral part of evidence-based decision-making processes and is being increasingly used in medical and non-medical disciplines. Aggregate data or summary statistics continue to be the mainstay of meta-analysis and are used by many professional societies to support clinical practice guidelines. Meta-analyses synthesize the summary statistics from independent trials by pooling them to estimate the underlying common effect size. The results represent the highest level of evidence but only if the chosen studies are of high quality and the selection criteria are fully satisfied. It is important to address the issues of defining an explicit and relevant question, exhaustively searching for the totality of evidence, meticulous and unbiased data transfer or extraction, assessment of between study heterogeneity and the use of appropriate statistical methods for estimating summary effect measures. This article reviews the methodology, benefits and drawbacks of performing a meta-analysis.