Statistical analysis
Meta-analysis was performed on crude data extracted from the text. We calculated the weighted mean difference (WMD) for continuous outcomes and the odds ratio (OR) for the dichotomous data, along with the 95% confidence intervals (CIs). In instances in which a standard error was not reported, we calculated the standard error of mean differences according to the methods described in Cochrane Handbook[13].
Prior to analyzing the data, heterogeneity was assessed by the Cochran Q test along with visual inspection of the forest plot. Then, it was quantified by I2 test. A fixed-effect model was used when the effects were assumed to be homogenous (P>0.05 or I2 <50 %)[13]. However, given that the clinical settings differed across studies, we assumed the presence of heterogeneity and used random-effects model in all subsequent analyses, for the outcome of which were more conservative as they consider differences both within and among studies in calculating the error term used in the analysis[13].
Funnel plots were employed for detection of publication bias, in which the effect sizes (e.g., OR or WMD) are plotted on the horizontal axis and its variance (e.g., the standard error of the log effect) on the vertical axis. Bias was revealed if the plots were asymmetrical about the pooled value.
All statistical analyses were done with Review Manager 5.3.5 (Cochrane Collaboration, Oxford, UK). Results were regarded as statistically significant if P<0.05.