Definition

Meta-analysis

The statistical pooling of effect sizes from multiple studies into one overall estimate, with heterogeneity quantified.

Each study contributes its effect size, weighted by precision (larger studies count more); the output is a pooled estimate with a confidence interval, usually shown in a forest plot. Random-effects models, the modern default, allow true effects to vary between studies; I² summarizes how much they do.

A meta-analysis is only as good as its systematic review: garbage in, precision-weighted garbage out. Publication bias checks (funnel plots) and sensitivity analyses are standard equipment, and high heterogeneity is a signal to explain (via moderators), not average away.