Table 1.

Demographic and occupational data on the study groups

	COPD group (n = 22)	Control group (n = 22)	P value
Age, years	50 ± 7	47 ± 5	NS
Length of service, years	26 ± 8	25 ± 8	NS
Cumulative exposure indices to silica dust	12 ± 19	11 ± 18	NS
Education, school years	8 ± 2	9 ± 3	NS
Smoking status, packs/year	547 ± 449	315 ± 210	NS

NS = Nonsignificant (p > 0.05). Four subjects in the control and none in the COPD group were never smokers.