Table 1.

Demographic data.

Gender (n, %)
˙Male	53 (38.1%)
˙Female	86 (61.8%)
Age (n, %)
˙no more than 18 years	25 (17.9%)
˙19 to 30 years	12 (8.6%)
˙31 to 40 years	30 (21.5%)
˙41 to 50 years	27 (19.4%)
˙51 to 60 years	23 (16.5%)
˙more than 60 years	22 (15.8%)
Permanent address(n, %)
˙Beijing	94 (67.6%)
˙Domestic(except Beijing)	44 (31.7%)
˙Oversea	1 (0.7%)
Smoking history(n, %)
˙History of smoking and still smoking	20 (14.3%)
˙History of smoking, quit smoking	10 (7.2%)
˙No history of smoking	109 (78.4%)