Table 2

Cox proportional hazards models predicting incident airflow limitation

	Univariate analysis		Multivariate model 1		Multivariate model 2
	HR (95% CI)	p Value	HR (95% CI)	p Value	HR (95% CI)	p Value
Sex: male	1.36 (1.10 to 1.68)	0.004	1.16 (0.92 to 1.45)	0.20	1.12 (0.89 to 1.40)	0.32
Age in years	1.04 (1.03 to 1.04)	<0.001	1.03 (1.02 to 1.04)	<0.001
Formal education: >12 years	0.58 (0.46 to 0.72)	<0.001	0.85 (0.68 to 1.07)	0.17	0.82 (0.65 to 1.03)	0.09
FEV₁/FVC ratio (%)	0.88 (0.86 to 0.89)	<0.001	0.89 (0.88 to 0.91)	<0.001	0.89 (0.87 to 0.91)	<0.001
Pack-years
<1 pack-year	Ref		Ref		Ref
1–19.9 pack-years	1.19 (0.90 to 1.59)	0.22	1.50 (1.12 to 2.01)	0.007	1.31 (0.98 to 1.76)	0.07
20–49.9 pack-years	2.79 (2.14 to 3.64)	<0.001	1.75 (1.32 to 2.32)	<0.001	1.73 (1.30 to 2.29)	<0.001
⩾50 pack-years	3.78 (2.64 to 5.40)	<0.001	2.28 (1.57 to 3.32)	<0.001	2.22 (1.52 to 3.24)	<0.001
Chronic bronchitis	1.94 (1.40 to 2.69)	<0.001	1.37 (0.98 to 1.92)	0.07	2.24* (1.33 to 3.76)	0.002
Categorical age: ⩾50 years					2.22 (1.71 to 2.89)	<0.001
Interaction term: chronic bronchitis×age ⩾50 years					0.41 (0.21 to 0.80)	0.009

All predictors were measured at the enrolment survey (1972–1973). n is 1410 because two subjects had missing information.
*This HR represents the increase in risk associated with chronic bronchitis among subjects <50 years old.
FEV₁, forced expiratory volume in 1 s; FVC, forced vital capacity.