Statistical analysis
A comprehensive meta-analysis was
performed to calculate Relative risk (RR) or mean difference and their
95% confidence interval (CI) by Revman 5.3. Statistical heterogeneity
was assessed by Cochran’s Q statistic and the I2statistic. The fixed-effects model was used to pool studies when
statistical heterogeneity was absent and when substantial heterogeneity
was defined as I2 >50% or chi-squared test P
<0.1; otherwise, the random-effects model was employed. For
individual trials with no events in one or both groups, a continuity
correction of 0.5 was added to each cell17,18.