Publication bias
The funnel plot of standard error vs. effect size was asymmetric and suggestive of potential publication bias. Presence of publication bias was also suggested by Egger’s linear regression (P = < 0.001). After adjustment of effect size for potential publication bias using the ‘trim and fill’ correction, fourteen potentially missing studies on the left side of the funnel plot were imputed leading to a corrected effect size that was slightly but not significantly less than the initial estimate (0.22 (95% CI 0.14-0.29, Figure 6).