Table 2: Differences in demographic, occupational and psycho-familial variables according to pain in the previous three months (n=674). Values are either n (%) or mean [SD].
Variables		Chronic pain		p value
Demographic variables		Yes (n=162)	No (n=512)
Age group (yrs)	18–30	43 (6.3)	192 (28.4)	0.03
	31–50	121 (18.0)	250 (37.1)
	>50	2 (0.4)	66 (9.8)
Sex	Male	152 (22.6)	460 (68.2)	0.33
	Female	12 (1.8)	50 (7.4)
Marital status	Single	13 (2.0)	146 (21.7)	< 0.001
	Married	50 (8.0)	360 (53.5)
	Divorced/Widowed	99 (14.0)	6 (0.8)
Education	High school or less	6 (0.9)	44 (6.6)	0.09
	Diploma	42 (6.3)	106 (15.7)
	Bachelor	84 (12.4)	258 (38.3)
	MSc/PhD	30 (4.4)	104 (15.4)
Occupational variables
Type of industry	Petrochemical	99 (14.7)	303 (45.0)	0.81
	Petroleum refinery	63 (9.3)	209 (31.0)
Type of job	White collar	34 (5.1)	125 (18.8)	0.77
	Gray collar	228 (4.3)	71 (10.7)
	Blue collar	54 (8.1)	152 22.9)
Daily work (hrs/day)	8 hours	12 (1.8)	41 (6.1)	0.58
	10 hours	36 (5.3)	124 (18.4)
	≥12 hours	114 (16.9)	347 (51.5)
Absence from work (hrs/month)		0.3 [0.9]	1.5 [2.1]	0.08
Work experience (yrs)		7.5 [4.1]	4.3 [6.7]	0.04
Scores of psycho-familial variables
Depression		9.6 [5.4]	7.5 [5.2]	<0.001
Work-family conflict		37.4 [12.7]	32.4 [14.4]	<0.001
Job stress		61.9 [20.0]	56.9 [21.8]	0.007