What is meta-analysis good for?

Abstract There is an ongoing debate about the quality of the evidence that meta-analysis provides. But both critics and defenders of meta-analysis generally assume that the core purpose and contribution of meta-analysis is to tell us what the evidence really says about the existence and magnitude of causal relationships, to extract conclusions that agree from datasets that do not. I argue that while delivering such information about cause-and-effect relationships is the most common use of meta-analysis, this is only an application of the tool, and that its primary epistemic role of meta-analysis is something else entirely: to help us explore and understand variation among populations of studies.