Incidence rate of obstruction (FEV1/FVC <0.7) using prebronchodilator spirometry during 11 years of follow-up according to a set of baseline characteristics
| Predictor at baseline | Person-years at risk (in 1000) | No. of cases | Incidence rate (cases per 1000 person years) (95% CI) | Crude incidence rate ratio (95% CI) | Adjusted‡ incidence rate ratio (95% CI) |
| All (n = 4945)* | 54.00 | 765 | 14.17 (13.20 to 15.21) | ||
| Gender: | |||||
| Men | 24.55 | 357 | 14.54 (13.11 to 16.13) | 1.00 (Ref) | 1.00 (Ref) |
| Women | 29.45 | 408 | 13.85 (12.57 to 15.27) | 0.95 (0.84 to 1.09) | 1.03 (0.90 to 1.18) |
| Age (years) at baseline | |||||
| 18–30 | 11.62 | 70 | 6.02 (4.77 to 7.61) | 1.00 (Ref) | 1.00 (Ref) |
| >30–40 | 14.70 | 165 | 11.22 (9.64 to 13.07) | 1.86 (1.43 to 2.43) | 1.72 (1.33 to 2.24) |
| >40–50 | 15.81 | 253 | 16.00 (14.15 to 18.10) | 2.66 (2.08 to 3.40) | 2.38 (1.85 to 3.06) |
| >50 | 11.86 | 277 | 23.35 (20.75 to 26.27) | 3.88 (3.05 to 4.93) | 3.77 (2.94 to 4.83) |
| Smoking status at baseline†: | |||||
| Never smoker | 28.02 | 362 | 12.92 (11.65 to 14.32) | 1.00 (Ref) | 1.00 (Ref) |
| Ever smoker: | |||||
| <15 pack-years | 14.94 | 153 | 10.24 (8.74 to 12.00) | 0.79 (0.66 to 0.95) | 0.87 (0.73 to 1.04) |
| ≥15 pack-years | 11.03 | 250 | 22.66 (20.02 to 25.65) | 1.75 (1.52 to 2.03) | 1.51 (1.29 to 1.77) |
| Chronic bronchitis at baseline: | |||||
| Absent | 49.62 | 671 | 13.52 (12.54 to 14.59) | 1.00 (Ref) | 1.00 (Ref) |
| Present | 4.38 | 94 | 21.45 (17.53 to 26.26) | 1.59 (1.30 to 1.93) | 1.23 (1.00 to 1.51) |
| Asthma at baseline | |||||
| Absent | 50.47 | 678 | 13.43 (12.46 to 14.48) | 1.00 (Ref) | 1.00 (Ref) |
| Present, but non-current | 2.34 | 54 | 23.12 (17.70 to 30.18) | 1.72 (1.33 to 2.22) | 1.39 (1.01 to 1.92) |
| Present, current | 1.18 | 33 | 28.02 (19.92 to 39.41) | 2.09 (1.51 to 2.88) | 0.79 (0.51 to 1.23) |
| Asthma at follow-up | |||||
| Absent | 49.75 | 662 | 13.31 (12.33 to 14.36) | 1.00 (Ref) | 1.00 (Ref) |
| Present, but non-current | 2.64 | 49 | 18.54 (14.01 to 24.53) | 1.39 (1.07 to 1.82) | 1.19 (0.85 to 1.65) |
| Present, current | 1.60 | 54 | 33.77 (25.86 to 44.09) | 2.54 (1.97 to 3.28) | 1.68 (1.13 to 2.50) |
| Wheezing without a cold at baseline | |||||
| Absent | 50.81 | 689 | 13.56 (12.59 to 14.61) | 1.00 (Ref) | 1.00 (Ref) |
| Present | 2.96 | 71 | 23.99 (19.01 to 30.27) | 1.77 (1.41 to 2.21) | 1.04 (0.81 to 1.35) |
| Wheezing without a cold at follow-up | |||||
| Absent | 50.34 | 655 | 13.01 (12.05 to 14.05) | 1.00 (Ref) | 1.00 (Ref) |
| Present | 3.65 | 110 | 30.10 (24.97 to 36.29) | 2.31 (1.92 to 2.79) | 1.95 (1.57 to 2.42) |
↵* Additional reduction of sample size due to exclusion of participants with >120 pack-years at baseline or >150 at follow-up.
↵† Smoking status at baseline: never smokers: <20 packs of cigarettes and <360 g of tobacco in lifetime.
↵‡ Adjusted for study area, educational level and all predictors listed in the table.
FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity.