Funnel Plot

A funnel plot is a scatter diagram plotting individual study effect sizes (x-axis) against a measure of study precision, typically standard error (y-axis, inverted). In the absence of bias, studies distribute symmetrically around the pooled effect estimate, forming an inverted funnel shape — large precise studies cluster near the top center, while smaller less precise studies scatter more widely at the bottom. Asymmetry in the funnel plot suggests publication bias (missing small negative studies) or other systematic biases. Visual assessment is subjective, so statistical tests (Egger's, Begg's) provide formal evaluation.