Table A2.

Variable assignment of independent variables of multiple linear regression analysis.

Variables	Assignment
Fiber exposure level	0 = Control group, 1 = Low exposure level, 2 = High exposure level
Total dust exposure level	0 = Control group, 1 = Low exposure level, 2 = High exposure level
Smoking status	0 = Never-smokers, 1 = Ever-smokers
Gender	0 = Female, 1 = Male
Age, years	Continuous variable