Pooled ORs and 95% CIs of the overall and stratified meta-analyses.

<p>OR: odds ratio; CI: confidence interval. The results were in bold, if the 95% CI excluded 1 or <i>P</i><0.05.</p>a<p>the statistical significance of the pooled OR was determined by the Z test;</p>b<p>No statistical significance was found by the heterogeneity test, then the fixed-effects model was adopted here.</p>c<p>confirmatory analyses with a random-effect model was used if there was significant heterogeneity.</p>d<p>when the dominant model was analyzed, the data studied by Wenzhang Wang (2011) was added.