A consumer's guide to meta-analysis.

The same proponent of meta-analysis who feels that it offers the highest level of evidence of treatment efficacy has also warned that "it is easy to do a meta-analysis; it is hard to do one well" (1). This paper has listed a series of issues that should be addressed in the construction of a good meta-analysis. A meta-analysis protocol needs to be prepared. A concerted effort should be made to capture all published and unpublished studies that address the research question. These studies should then be compared to the inclusion and exclusion criteria from the protocol to determine which will be used in the meta-analysis. A random effects analysis should be performed on the studies. A test of the homogeneity of studies should be done. Funnel plots and the tolerance for null results should be computed to assess publication biases. Finally, sensitivity analyses should be performed. All of these issues need to be discussed in the report of the meta-analysis so that readers can judge the validity of the conclusions.