Systematic reviews and meta-analysis: studies of studies.

Systematic reviews are designed to answer a focused clinical question. They employ a predetermined explicit methodology to comprehensively search for, select, appraise, and analyze studies. Meta-analysis is the statistical pooling of the results of studies that are part of a systematic review. Systematic reviews are research studies and, like other studies, they need to be based on a structured and valid methodology and take measures to minimize bias. High-quality systematic reviews can be powerful tools to support clinical decision-making, as well as summarize current knowledge in relation to an area of research interest. This article describes the methodology that should be used when doing a systematic review, presents guidelines for reporting the review, and provides a guideline for critically appraising published reviews.