Table 3.

Incidence rate ratios (IRRs) with 95% CIs for the association between increasing airway responsiveness and the development of COPD: sensitivity analyses on the outcome definition*

Slope group, by quintiles (% × µmol−1)	COPDclinical	COPD0.70
No of subjects	3743	3565
<0.45	1.0	1.0
0.45–0.74	1.52 (0.44 to 5.33)	0.75 (0.47 to 1.20)
0.75–1.13	2.64 (0.97 to 7.22)	1.50 (1.10 to 2.04)
1.14–1.85	5.18 (2.21 to 12.14)	2.10 (1.51 to 2.93)
>1.85	7.64 (3.38 to 17.27)	2.92 (1.99 to 4.28)

*Adjusted for study, sex, education, FEV₁ predicted, age, body mass index, history of asthma/asthma-like symptoms, history of active smoking, second-hand smoking and occupational exposures to vapours, gas, dusts or fumes.