Table 1 Selected characteristics of the exposed and control groups in a steel plant in northern China.

Variables	Control group	Exposed group	p Value
Number of subjects	102	207
Age (years, mean (SD))	37.0 (5.0)	37.5 (6.4)	0.471*
Employment time (years, mean (SD))	16.4 (6.3)	15.9 (7.5)	0.565*
Current smokers, yes (%)	80 (78.4%)	166 (80.2%)	0.719**
Pack‐years (years, mean (SD))	13.0 (14.4)	15.6 (14.0)	0.037***
Alcohol users, yes (%)	50 (49.0%)	104 (50.2%)	0.903**
Eight carcinogenic PAHs (median levels, range)	0.306 (0.233–0.350)	0.852 (0.259–3.330)	0.008***
B[a]P (median levels, range)	0.040 (0.020–0.060)	0.100 (0.028–0.360)	0.014***

*Student t test for difference in quantitative measurements between the exposed and control groups.

**χ² tests for differences in the distribution between the exposed and control groups.

***Mann‐Whitney U test for differences between the exposed and control groups.