Table 1. The baseline characteristics of study population.
| Characteristics | Patients (n = 684) | Controls (n = 602) | P** |
| Age (years) | 57.24 (9.84) | 56.80 (9.95) | 0.776 |
| Sex (male) | 72.78% | 66.49% | 0.013 |
| Smoking | |||
| Current | 28.22% | 6.99% | |
| Ever | 8.04% | 0.54% | <0.005 |
| None | 63.74% | 92.47% | |
| Drinking | |||
| Current | 15.23% | 5.38% | |
| Ever | 1.61% | 2.69% | <0.005 |
| None | 83.16% | 91.94% | |
| Lung cancer type | |||
| Squamous cell cancer | 32.26% | −* | |
| Adenocarcinoma | 37.54% | − | |
| Small cell cancer | 20.83% | − | |
| Unspecified | 9.38% | − |
Data are expressed as mean (standard deviation or SD) or percentage as indicated. * data not available. **P values were calculated by using unpaired t-test for age, and by χ2 test for other categorical characteristics.