Heterogeneity across the publications was assessed with the Cochran's ,chi. 2 test (Q-test) [26] , and p,0.10 was considered statistically significant. The I 2 test was also conducted to evaluate heterogeneity between studies. A high heterogeneity is considered present when I 2 .50% and much higher when I 2 .75% [27] . The pooled OR was calculated by a fixed effect model (using the Mantel-Haenszel method) or a random effect model (using the DerSimonian-Laird method) according to the heterogeneity among studies [28] . The statistical significance of OR was analyzed by the Z test, and p,0.05 was considered statistically significant. Publication bias was evaluated by Egger's and Begg's tests and was considered significant if p,0.05 [29, 30] . Sensitivity analysis was performed by sequentially excluding individual studies to assess the stability of the results.