Table 6. Results of multiple stepwise regression analysis for QOL.

Dependent variable	Independent variable	Regression coefficient	Standardized regression coefficient	t	P
Underground miners
Total score	Chronic disease	−56.717	−0.109	−2.703	0.007
PHC	Job tenure for dust exposure	−8.290	−0.116	−2.850	0.005
	Chronic disease	−21.106	−0.093	−2.302	0.022
MHC	Chronic disease	−23.629	−0.097	−2.407	0.016
	Education level	−13.459	−0.090	−2.224	0.027
Ground workers
Total score	Medical insurance	−62.898	−0.243	−4.819	<0.001
	Education level	55.598	0.220	4.328	<0.001
	Chronic disease	−41.804	−0.126	−2.495	0.013
PHC	Age	−16.559	−0.121	−2.093	0.037
	Chronic disease	−31.514	−0.183	−3.612	<0.001
	Medical insurance	−24.365	−0.181	−3.667	<0.001
	Education level	21.093	0.161	2.829	0.005
	Average monthly income	17.931	0.113	2.253	0.025
MHC	Medical insurance	−36.533	−0.245	−4.766	<0.001
	Education level	24.951	0.171	3.332	0.001

QOL, quality of life; PHC, physical health components; MHC, mental health components.