Data synthesis and analysis
We calculated the standardized summary mean differences and the relative risks (RR), along with the corresponding 95% CI, by pooling the study-specific estimates using fixed and random-effects models. The standardized mean difference indicated the mean change per SD allowing for the comparison of scores in different scales. The presence and the degree of heterogeneity were assessed with I2 (ranging from 0% to 100%). When high heterogeneity was detected, it was further investigated through subgroup analysis. We further assessed possible small study effects (an indication of publication bias) by visual inspection of funnel plots and Egger test. All analyses were performed using Stata (version 14; StataCorp, College Station, TX, USA).