2.5 Statistical analysis
Binary variables were expressed as odds ratios (ORs) with 95%
confidence intervals (CIs). Continuous variables were analyzed using the
mean difference (MD) and the corresponding 95% CI estimated using the
inverse-variance method. A two-sided P-value≤0.05 was considered
statistically significant. The fixed-effects model and the
random-effects model were considered based on the level of
heterogeneity. The heterogeneity of studies was evaluated by Cochran’s Q
and the I2 statistic. I2 lies
between 0% and 100% with larger values showing increasing
heterogeneity. I2 value >50% was
considered high degrees of heterogeneity and the random model was used
in the subgroup analysis or sensitivity analysis excluding the trials
that potentially biased the results to avoid publication bias,
otherwise, a fixed-effects model was used 13,14. We
performed sensitivity analysis by omitting one study successively to
evaluate the impact of the individual studies on the pooled effect
size. All statistical analyses were performed using the RevMan version
5.3 (Nordic Cochrane Center; The Cochrane Collaboration, 2014).