Table 3 Poisson regression analysis: trend in lung cancer risk across tertiles of length of employment (Duration) adjusted for age and calendar period in the sub-cohort of carders: incidence rate ratio (IRR) and 95% CI

Terms	IRR	95% CI	2-sided p Value
Duration	0.35	0.13 to 0.95	0.040
Age
<49 years	Reference
50–59 years	13.26	2.13 to 82.51	0.006
⩾60 years	9.39	0.97 to 90.84	0.053
Calendar period
1970–9	Reference
1980–9	1.29	0.24 to 6.97	0.767
1990–4	1.88	0.34 to 10.43	0.471