While the main focus of this chapter will be meta-analysis, it cannot be completely isolated from several prerequisites assessed in the systematic review. For example, the studies must address a common question. The eligibility criteria of the underlying studies must be well established. Evaluation techniques for endpoints must be reasonably consistent across the studies. In the clinical setting, when making comparisons between a treatment and control, the underlying studies must be properly randomized. Exploratory meta-analyses and meta-regressions may examine associations between interventions, covariates, and secondary events. © 2010 Springer-Verlag Berlin Heidelberg.