Baseline characteristics according to change in severity of obstruction* during follow-up
| Persistently normal | Incident stage I | Incident stage II | Persistent stage I | Stage I progressing | Persistent stage II | Non-persistent | |
| n = 4181 | n = 683 | n = 85 | n = 294 | n = 56 | n = 61 | n = 113 | |
| Female sex (%) | 54.7 | 54.2 | 44.7 | 39.1 | 33.9 | 32.8 | 40.7 |
| Age in years (mean/SD) | 39.2/11.2 | 45.3/10.3 | 44.5/11.9 | 48.8/9.6 | 48.5/9.2 | 49.5/9.1 | 47.0/9.1 |
| No professional education (%) | 12.1 | 16.4 | 23.5 | 15.6 | 21.4 | 19.7 | 8.8 |
| FEV1 % of predicted value (mean/SD) | 109.9/13.6 | 107.4/12.5 | 91.3/12.5 | 101.3/10.9 | 89.1/7.0 | 67.4/10.4 | 99.6/13.5 |
| FVC % of predicted value (mean/SD) | 114.0/0.2 | 119.2/0.1 | 100.6/0.1 | 125.9/0.1 | 116.0/0.1 | 96.0/0.1 | 122.4/0.2 |
| FEV1/FVC % of predicted value (mean/SD) | 100.9/0.1 | 94.6/0.1 | 94.9/0.1 | 84.1/0.0 | 80.2/0.1 | 73.3/0.1 | 84.8/0.0 |
| Never smoker (%) | 49.9 | 44.7 | 35.3 | 36.7 | 19.6 | 31.1 | 38.9 |
| Light smoker at baseline (<15 pack-years)† (%) | 28.7 | 19.3 | 13.6 | 20.9 | 9.3 | 11.8 | 24.5 |
| Heavy smoker at baseline (≥15 pack-years)† (%) | 18.2 | 31.8 | 42.4 | 38.4 | 62.5 | 52.5 | 29.2 |
| Shortness of breath at baseline (%) | 21.7 | 25.0 | 42.4 | 25.5 | 44.6 | 47.5 | 14.2 |
| Chronic bronchitis at baseline (%) | 7.3 | 11.6 | 20.0 | 13.3 | 19.6 | 27.9 | 9.7 |
| Wheezing in last 12 months at baseline | 4.8 | 7.8 | 22.4 | 9.9 | 28.6 | 20.0 | 8.0 |
| Non-current asthma at baseline (%) | 5.6 | 10.5 | 17.6 | 12.2 | 21.4 | 27.9 | 9.7 |
| Current asthma at baseline (%) | 1.8 | 3.4 | 11.8 | 4.4 | 16.1 | 16.4 | 4.4 |
| Health service use for respiratory problems at baseline (%) | 18.0 | 22.0 | 27.1 | 26.9 | 33.9 | 42.6 | 23.0 |