Table 4

Effect of adjustment for asbestos exposure on association between lung cancer sand silica exposure

				Not adjusted for asbestos exposure		Adjusted for asbestos exposure^*
		Cases	Person years	RR^†	95% CI	RR^†	95% CI
Duration of silica exposure	Per 10 year	687	9984	1.16	1.00 to 1.35	1.20	0.97 to 1.48
	1 to 10 years	23	318	1.12	0.59 to 2.13	1.13	0.59 to 2.15
	11 to 25 years	24	269	0.97	0.52 to 1.82	1.04	0.53 to 2.04
	26 to 51 years	49	309	2.00	1.12 to 3.58	2.28	1.06 to 4.87

Cumulative silica exposure	Per 1 mg/m³.year	687	9984	1.12	1.01 to 1.25	1.13	0.99 to 1.29
	>0 to <3 mg/m³.year	40	478	1.04	0.63 to 1.72	1.07	0.64 to 1.79
	≥3 mg/m³.year	56	417	1.82	1.09 to 3.04	2.01	1.05 to 3.84

↵* Weighted for asbestos exposure probability.
↵† Population restricted as in table 3 plus non-exposed limited to white collar workers. Associations adjusted for age (years), family history of lung cancer (yes/no), current smoker status (yes/no), number of cigarettes smoked per day, years of smoking cigarettes, consumption of fruit and vegetables (g/d) and alcohol consumption (0–30 g/d, ≥30 g/d).