Meta-analysis is a statistical procedure for combining the results of several studies that address a set of similar research questions. It is commonly used to underpin systematic reviews of prevention programs. For example, the results of several RCTs of cognitive behavior programs to reduce phobias may be subjected to a meta-analysis revealing the combined effect of the intervention. The quality of any meta-analysis reflects the quality of studies included; no matter how skilful, meta-analysis of poor datasets will result in unreliable results.