Subject distributions by number of lung function tests and by follow up duration
| Group | Total | ||||
|---|---|---|---|---|---|
| Operation | Maintenance | Electricity | Other | ||
| Number of lung function tests | |||||
| 2–3 | 74 (20.3%) | 31 (30.1%) | 10 (17.0%) | 25 (47.2%) | 140 |
| 4–5 | 80 (21.9%) | 23 (22.3%) | 13 (22.0%) | 15 (28.3%) | 131 |
| 6–10 | 129 (35.3%) | 30 (29.1%) | 30 (50.8%) | 12 (22.6%) | 201 |
| 11–12 | 82 (22.5%) | 19 (18.5%) | 6 (10.2%) | 1 (1.9%) | 108 |
| Follow up duration (years) | |||||
| 0− | 37 (10.1%) | 11 (10.6%) | 7 (11.9%) | 23 (43.4%) | 78 |
| 3− | 50 (13.7%) | 20 (19.4%) | 7 (11.9%) | 12 (22.6%) | 89 |
| 5− | 147 (40.3%) | 36 (35.0%) | 28 (47.4%) | 14 (26.4%) | 225 |
| ⩾10 | 131 (35.9%) | 36 (35.0%) | 17 (28.8%) | 4 (7.6%) | 188 |
| Total | 365 | 103 | 59 | 53 | 580 |