All statistical analyses were performed using SPSS 21.0 (SPSS Inc. USA) software package. Unless special comments, all the data are the average + / - standard deviation (SD) or percentages. The subjects in the data measurement data, such as age, smoking index, FEV1 percentage of expected value, FEV1 / FVC, enzyme activity, antioxidant ability index, etc., use group t test were compared between groups (alpha = 0.05), group comparison before and after using matching t test. Counting data, such as gender, were compared using the Chi-square test. The frequency of GSTM1 and GSTM3 polymorphisms between different groups was compared using a two-tailed chi-square test. Bilateral test was used for all statistical results, and P < 0.05 was considered statistically significant.