Demographic characteristics, smoking and lung function
| Variable | Total (n = 3802) |
| Gender, men, n (%) | 1797 (47.3) |
| Age, mean (SD) | 56.6 (10.7) |
| BMI, mean (SD) | 27.4 (4.5) |
| Smoking history, n (%) | |
| Smoker | 989 (26.0) |
| Ex-smoker | 174 (30.9) |
| Never smoker | 1635 (43.1) |
| Pack-years (smokers and ex-smokers) | 26.0 (21.5) |
| Education, n (%) | |
| Less than primary school | 358 (9.4) |
| Primary school | 1393 (36.7) |
| Secondary school | 1105 (29.1) |
| University degree | 912 (24.0) |
| Missing | 30 (0.8) |
| Spirometry (postbronchodilator) | |
| FVC (litres) | 3.74 (1.0) |
| FVC (% predicted) | 96.8 (16.3) |
| FEV1 (litres) | 2.94 (0.9) |
| FEV1 (% predicted) | 102.1 (19.4) |
| FEV1/FVC | 0.79 (0.08) |
| Previous diagnosis of COPD, chronic bronchitis or emphysema, n (%) | 203 (5.3) |
| Previous diagnosis of asthma, n (%) | 261 (6.9) |
| City size: | |
| Small (<100 000 inhabitants) | 1078 (28.3%) |
| Medium (100 000–500 000) | 1268 (33.3%) |
| Large (>500 000) | 1456 (38.3%) |
BMI, body mass index; COPD, chronic obstructive pulmonary disease. FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity.