Table 1. Characteristics of participants related to adjustment factors comparing job categories using the chi-squared test.

Adjustment factors		Professional drivers			White-collar workers
		n	%		n	%	P values
Age group (years)	30–49	297	50.2		183	55.8	0.113
	50–69	295	49.8		145	44.2
Annual family income	<4 million yen	232	39.2		94	28.7	0.002
	≥4 million yen	360	60.8		234	71.3
Working hours	<8 h	118	19.9		120	36.6	<0.001
	≥8 h	474	80.1		208	63.4
Shift work	No	308	52.0		242	73.8	<0.001
	Yes	284	48.0		86	26.2
Duration of employment	<10 years	368	62.2		179	54.6	0.030
	≥10 years	224	37.8		149	45.4
Night work	No	454	76.7		255	77.7	0.744
	Yes	138	23.3		73	22.3