A practical guide to meta-analysis.

The wealth of medical research published on a yearly basis demands methods to summarize the literature. Narrative or expert reviews were the traditional method to provide this summary; however, biases associated with narrative reviews raise questions regarding whether this process provides sufficient evidence to guide practice. Meta-analysis is becoming increasingly popular because it can combine results from similar studies to calculate an overall estimate of a treatment effect. Although meta-analysis has its limitations, a thoughtful and well-planned analysis is a valuable tool in providing a high level of evidence. We discuss the steps needed to perform a meta-analysis as a guideline for those interested in pursuing this type of research.