What is a meta-analysis?

A meta-analysis combines the numerical results of several comparable studies into a single overall estimate, weighting each study by its precision. It is often the quantitative part of a systematic review. It needs each study’s effect size and uncertainty, so careful data extraction, with the page each number came from, is essential.

Heterogeneity, how much studies disagree, decides whether pooling is meaningful.

When studies are too different to pool, a narrative synthesis is the honest alternative.