Statistical analysis
Statistical meta-analysis was performed using the RevMan 5.3 software
(Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration,
2011). Confidence intervals (CI) were set at 95%. Mean difference (MD)
and odds ratios (OR) were used in the analysis. The results were
calculated using the DerSimonian-Laird random effect model (REM)
revealing significant heterogeneity in the methodological
characteristics of the included studies19. The cut-off
for statistical significance was set at p<0.05. Mean values
and standard deviations were calculated according to the equations
proposed by Hozo et al when not provided by the
studies20. To assess the between-study heterogeneity
more precisely, both the Chi-square based Q statistic test for
heterogeneity and the I2 statistic to quantify the
proportion of the total variation attributable to heterogeneity were
calculated. When there was no statistically significant heterogeneity
(p>0.05, I2<50%), a fixed
effect model was adopted. Otherwise, a random effect model was
chosen21. The heterogeneity was considered
statistically significant if a p<0.05. Publication bias was
not tested due to heterogeneity of the included studies, which is a
confounder that may influence the methodological integrity of these
tests.