Table 4.

Incidence rate ratios (IRR) and 95% CIs for lung cancer among 1166 ever-smoking Norwegian long-term silicon carbide (SiC) industry workers employed during 1913–2003 and followed up during 1953–2008, by tertiles of cumulative exposure, and with exposure lagging 0 and 20 years

	No lag				20 years lag of exposure
	Obs	IRR*	95% CI	ptrend	Obs	IRR*	95% CI	ptrend
Total dust (mg × years/m3)
0–30	9	1.0			21	1.0
30–87	13	1.0	0.4 to 2.4		12	1.4	0.7 to 3.0
87–900	36	1.9	0.9 to 4.0	p=0.04	25	3.0	1.6 to 5.6	p=0.001
Respirable dust (mg × years/m3)
0–3.8	8	1.0			23	1.0
3.8–10	18	1.7	0.7 to 4.0		14	1.6	0.8 to 3.2
10–87	32	2.0	0.9 to 4.4	p=0.09	21	2.4	1.3 to 4.6	p=0.007
Quartz (mg × years/m3)
0–0.026	10	1.0			25	1.0
0.026–0.077	18	1.3	0.6 to 2.8		16	1.5	0.8 to 2.9
0.077–2.3	30	1.5	0.7 to 3.1	p=0.3	17	1.5	0.8 to 2.8	p=0.2
Cristobalite (mg × years/m3)
0–0.028	9	1.0			21	1.0
0.028–0.093	15	1.2	0.5 to 2.7		18	2.0	1.0 to 3.9
0.093–2.7	34	2.0	0.9 to 4.1	p=0.04	19	2.2	1.1 to 4.1	p=0.02
SiC (mg × years/m3)
0–0.83	14	1.0			26	1.0
0.83–3.0	12	0.7	0.3 to 1.5		11	1.0	0.5 to 2.1
3.0–60	32	1.4	0.7 to 2.6	p=0.2	21	2.2	1.2 to 4.1	p=0.02
Fibres (fibres × years/cm3)
0–0.50	11	1.0			21	1.0
0.50–2.0	14	1.0	0.5 to 2.2		14	1.4	0.7 to 2.9
2.0–93	33	1.7	0.8 to 3.3	p=0.1	23	2.3	1.2 to 4.4	p=0.009

^*Adjusted for age (0–54/55–74/≥75).

Obs, observed number of cases.