Publication bias
Publication bias was evaluated graphically by inspecting the asymmetry of the funnel plots and statistically using Egger’s regression tests (Sterne & Egger 2005). Significantly asymmetric results were then augmented using the Trim and Fill method (Duval & Tweedie 2000). The Trim and Fill method estimates the number of missing studies due to publication biases, calculates their effect sizes and standard errors and adds them to the meta-analysis dataset. In addition, the Rosenberg’s fail-safe number was calculated. Rosenberg’s fail-safe number represents the number of non-significant, unpublished studies that must be added to a meta-analysis to change the result from significant to non-significant (Rosenberg 2005). A fail-safe number that is larger than 5n + 10, where n is the number of studies used in the meta-analysis, is considered robust (Rosenthal 1986).