A systematic review is a thorough and explicit way of searching the medical literature.

A meta-analysis combines the results of two or more studies identified through a systematic review and estimates a common effect. Meta-analysis should be based on a systematic review, but not every systematic review leads to a meta-analysis.

Statistical heterogeneity arises when meta-analysis combines studies whose results differ considerably. Heterogeneity can be statistically tested through the test of homogeneity or the I² test.