Table 1.

Baseline data.

Variables		n	%
Gender	Male	1,220	92.1
	Female	105	7.9
Age (years)	<30	171	12.9
	30+	254	19.2
	40+	609	46
	50+	291	22
Years of service	<10	402	30.3
	10+	305	23
	20+	618	46.6
Education	Junior high school or lower	581	43.8
	Senior high school or technical secondary	418	31.5
	Junior college	244	18.4
	Bachelor's degree or higher	82	6.2
Type of work	Coal miner	231	17.4
	Coal caver	26	2
	Coal drivage worker	238	18
	Anchor worker	11	0.8
	Craft worker	26	2
	Inspection worker	31	2.3
	Ventilation worker	48	3.6
	Gangue collector	21	1.6
	Electric locomotive driver	26	2
	Bell man	38	2.9
	Electrical fitter	158	11.9
	Plugman	18	1.4
	Operator	42	3.2
	Blaster	20	1.5
	Gas inspector	27	2
	Backman	49	3.7
	Monitor observer	22	1.7
	Loading workman	25	1.9
	Others	266	20.1
Shift system	Day shift only	490	37
	Two shifts	187	14.1
	Two shifts with three groups	536	40.5
	Three shifts with four groups	112	8.5
Marital status	Unmarried	126	9.5
	Married	1,156	87.2
	Divorced or widowed	43	3.2