Stata package version 12

Statistical analysis was conducted using the Stata package version 12.0 (Stata Corporation, College Station, TX, USA). The χ 2 -test was used for determining the HWE of genotypes and the heterogeneity of rare allele frequencies in the control groups of each study reviewed. The association of XPA A23G polymorphism and esophageal cancer risk was estimated by odds ratios (ORs) with 95% confidence intervals (95% CIs). Depending on the results of the heterogeneity test among individual studies, the fixed-effect model (Mantel-Haenszel) or random-effect model (DerSimonian and Laird) was selected to summarize the pooled ORs and their 95% CIs.
The significance of the pooled OR was determined by a Z-test. Sensitivity analysis was evaluated by comparing the results of fixed-effects model and random-effects model. We also performed stratification analyses by geographic area(s) and source of controls. P <0.05 was considered to be statistically significant.

We assessed HWE in the controls for each study using a chi-square test, and P < 0.05 was considered to indicate significant disequilibrium. The pooled odds ratio (OR) with corresponding 95% confidence interval (95%CI) was calculated to assess the strength of the association between the XRCC3 T241M polymorphism and CRC risk under homozygote comparison (TT vs MM), heterozygote comparison (TT vs MT), a dominant model (MM + MT vs TT), and a recessive model (TT + MT vs MM) between groups. Between-study heterogeneity was estimated using the I 2 test. I 2 ranges from 0-100% and represents the proportion of interstudy variability that can be attributed to heterogeneity rather than to chance. I 2 values of 25, 50, and 75% were defined as low, moderate, and high estimates, respectively. I 2 > 50% indicated heterogeneity across studies, and the random effects model was used for meta-analysis; otherwise, the fixed effects model was used. Subgroup analyses were performed by ethnicity and sample sizes. Sensitivity analysis was performed by removing the studies not in HWE. Funnel plot asymmetry was assessed by Begg's test to estimate potential publication bias (P < 0.05 indicated statistical significance). Meta-analysis was performed using the STATA package version 12.0 (Stata Corporation, College Station, TX, USA).