Table 3.

Dose-response effect of smoking on the risk of severe pulmonary fibrosis

Smoking, pack-years*	PF OR (95% CI)	IPF OR (95% CI)
0	1	1
1–9	1.03 (0.62 to 1.70)	0.90 (0.52 to 1.57)
10–19	2.26 (1.35 to 3.80)	2.10 (1.20 to 3.68)
≥20	2.66 (1.56 to 4.55)	2.25 (1.26 to 4.02)

ORs for levels of smoking estimated using conditional logistic regression adjusted for age and stratified for year of birth, year of diagnosis, gender and occupational exposure.

*Pack-years of smoking up to 10 years before the year of PF diagnosis.

IPF, idiopathic pulmonary fibrosis; PF, pulmonary fibrosis.