Evidence-based health care is becoming increasingly popular and, at least in some settings, is being used to assist in the creation of health care policy.1 Meta-analyses are a key component of evidence-based health care. Such analyses pool individual randomized controlled trials (RCTs) together to arrive at an overall estimate of the effect of the intervention under consideration. Meta-analyses offer several potential advantages. They provide a systematic and explicit method for synthesizing evidence, a quantitative overall estimate (and confidence intervals) derived from the individual studies, and early evidence as to the effectiveness of treatments, thus reducing the need for continued study. They also can address questions in specific subgroups that individual studies may not have examined.
There has been a striking increase in the number of published meta-analyses of RCTs. One of the first medical metaanalyses was published in JAMA in 1955.2 By June 1992, the number of meta-analyses