Comparison of the cross-sectional (n=1,942) and longitudinal (n=952) populations with chest radiographs
| Cross-sectional survey I | Longitudinal cohort | |
| Age yrs | 42 | 38 |
| Duration of employment months | 178.0 | 162.2 |
| % Females | 6.9 | 6.5 |
| % Smokers | 50.6 | 51.2 |
| % Exsmokers | 27.0 | 25.9 |
| Current inhalable mg·m−3 | 1.6 | 1.6 |
| Cumulative inhalable mg·month·m−3 | 299.1 | 279.0 |
| Small opacities# | 12.5 | 10.4 |
| Cough % | 17.8 | 15.1 |
| Sputum % | 17.2 | 17.2 |
| Cough with sputum % | 10.1 | 9.2 |
| Wheezing | 8.5 | 8.1 |
| Dyspnoea 2+ | 3.4 | 1.9 |
| Breathlessness with wheezing | 3.4 | 3.2 |
| Chronic bronchitis | 4.9 | 4.5 |
| FVC % pred | 108.8 | 110.9 |
| FEV1 % pred | 104.1 | 105.9 |
| FEF25–75 % pred | 85.6 | 87.3 |
| FEV1:FVC % pred | 91.4 | 91.8 |
FVC: forced vital capacity
FEV1: forced expiratory volume in one second
FEF25–75: forced midexpiratory flow
#: prevalence of small opacities (International Labour Organisation category ≥1/0) given here is based upon the original survey readings