2.5 Data extraction
The Stata software application (version 12.0; StataCorp, College
Station, TX) was used for data synthesis and analysis. Risk ratios (RR)
and 95% confidence intervals (CI) were calculated; pooled RR and 95%
CI were calculated using a fixed-effects model if the homogeneity
assumption was not rejected (P > 0.1, I2< 50%). If not, used the random effects model.
Chi-square-based Q statistic was used for subgroup analysis based on
between-trial heterogeneity, and statistical significance was considered
when the p-value was less than 0.05 or I2 was greater
than 50%.