Percentage of population with lung function below the lower limit of normal in “healthy” population for the Health Survey for England reference curves using different estimates of the 5th percentile by sex and age group
| Age yrs | Present model# | Mean – 1.645σ | ||
| FEV1 | FVC | FEV1 | FVC | |
| Males | ||||
| 16–24 | 4.0 | 5.0 | 4.5 | 4.0 |
| 25–34 | 5.8 | 5.0 | 5.0 | 3.9 |
| 35–44 | 6.3 | 6.0 | 5.3 | 6.3 |
| 45–54 | 3.5 | 5.1 | 4.3 | 6.6 |
| 55–64 | 3.1 | 3.8 | 6.9 | 6.9 |
| 65–74 | 6.4 | 6.4 | 12.1 | 10.8 |
| ≥75 | 5.1 | 5.1 | 8.5 | 15.3 |
| All | 5.0 | 5.2 | 5.6 | 5.9 |
| Females | ||||
| 16–24 | 5.5 | 6.1 | 3.0 | 3.7 |
| 25–34 | 4.6 | 5.7 | 3.2 | 3.2 |
| 35–44 | 6.3 | 4.4 | 4.9 | 4.1 |
| 45–54 | 5.1 | 5.4 | 5.6 | 5.9 |
| 55–64 | 5.3 | 6.7 | 6.5 | 7.9 |
| 65–74 | 5.5 | 5.2 | 10.9 | 9.1 |
| ≥75 | 5.7 | 3.8 | 13.8 | 10.7 |
| All | 5.4 | 5.4 | 5.5 | 5.4 |
σ: sd of residuals
FEV1: forced expiratory volume in one second
FVC: forced vital capacity
#: lower limit of normal=eb0+b1A+b2A2+b3ln H
coefficient values given in table 2⇑