Using meta-analysis in psychiatric research.

Meta-analysis is a technique for summarizing the results of many studies which can allow reviewers in a particular field to arrive at a synthesis of the various findings in a more objective manner than relying on expert opinion and combine the results of these studies to arrive at an overall estimate of the magnitude of the effect of a treatment, to determine if the evidence favours its effectiveness. The technique consists of determining an effect size or odds ratio for each study and combining them, taking into account the fact that studies with large samples should exert more influence than those with small samples. However, the procedure is not mechanical. The reviewer must make a series of decisions regarding the studies to be included or excluded, the weight to place on the methodological rigour of the trials, the results from each study to be used, how to handle differences in the magnitude of the results across studies, how to derive the best overall estimate of the effect across studies, and how to determine the precision of that estimate. Each of these decisions can affect both the quality of the review and the nature of the findings.