Assessment of publication bias.

Visual inspection of funnel (A) and precision (B) plots suggested an underrepresentation of studies with moderate precision and small effect sizes, but this was not confirmed by trim and fill analysis. Dotted line represents the overall effect size of 24.6. C-D: Egger's regression test revealed that small study effects are likely present, since the regression line does not intercept at the origin. ES = effect size; SE = standard error; MD = raw difference in means.