Table 2

Distribution of potential confounding factors

	Subjects	Current smokers (%)	Schooling >10 y (%)	Atopy (%)	Mean height (cm)	Mean age (y)
Refineries:
Refinery 1	927	22	47	42	176.6	41.3
Refinery 2	1005	23	48	50	176.9	39.6
Refinery 3	456	27	51	37	177.1	37.3
p Value^2-150		0.07	0.41	<0.001	0.31	<0.001
Process groups:
Office or administration	519	15	72	48	177.5	41.5
Powerhouse	106	19	39	34	175.3	45.9
Maintenance	897	25	42	47	176.6	38.2
Digestion	205	30	39	40	176.8	39.3
Clarification	202	33	45	37	177.0	39.8
Precipitation	152	24	41	43	177.4	39.6
Calcination or shipping	186	23	41	43	176.9	40.8
Residue	39	21	36	49	176.7	43.7
Descale	82	32	39	40	176.4	36.6
p Value^2-150		<0.001	<0.001	0.02	0.11	<0.001

↵2-150 χ² Test for difference in proportions orF test for difference in means between groups.