Table 4. Comparisons of the expression levels of Bcl-2, Caspase-3 and Caspase-8 among different subgroups based on age, smoking, initial working time, occupational time, and working age for occurrence in the exposed group.

Group	N	Bcl-2	Caspase-3	Caspase-8
Age
< 40	156	0.356 ± 0.047	0.354 ± 0.047	0.032 ± 0.045
≥ 40	210	0.310 ± 0.035*	0.322 ± 0.042*	0.038 ± 0.043
Smoking (duration time, years)
0	165	0.345 ± 0.054	0.401 ± 0.054	0.376 ± 0.050
< 30	88	0.336 ± 0.048	0.367 ± 0.041*	0.382 ± 0.056
≥ 30	113	0.342 ± 0.043	0.375 ± 0.050*	0.367 ± 0.048
Initial working time (years)
< 20	144	0.288 ± 0.043	0.376 ± 0.055	0.256 ± 0.035
≥ 20	222	0.231 ± 0.034*	0.345 ± 0.036*	0.218 ± 0.040*
Working years (years)
< 20	170	0.288 ± 0.060	0.377 ± 0.062	0.236 ± 0.056
≥ 20	196	0.243 ± 0.051*	0.332 ± 0.054*	0.228 ± 0.047
Working age for occurrence
< 10	130	0.227 ± 0.057	0.376 ± 0.067	0.321 ± 0.046
≥ 10	136	0.234 ± 0.048	0.337 ± 0.068*	0.327 ± 0.050

Note: ^*P < 0.05 when compared between two subgroups.