Percentage of explained variance of existing reference equations on our datasets
| Males | Females | |||||
| Training | Internal validation | External validation | Training | Internal validation | External validation | |
| Quanjer [12] | ||||||
| FEF25 L·s−1 | 8.49 | 10.1 | 7.01 | 14.5 | 15.6 | 11.2 |
| FEF50 L·s−1 | 19.1 | 19.3 | 18.0 | 26.7 | 27.4 | 27.6 |
| FEF75 L·s−1 | 43.4 | 43.0 | 55.1 | 50.9 | 51.3 | 56.3 |
| FEF25–75 L·s−1 | 32.3 | 30.6 | 37.2 | 41.9 | 42.3 | 42.1 |
| GLI [13] | ||||||
| FEF75 L·s−1 | 47.4 | 46.3 | 55.1 | 53.0 | 53.6 | 58.3 |
| FEF25–75 L·s−1 | 32.8 | 32.0 | 38.2 | 42.5 | 42.7 | 42.9 |
Data are presented as %. FEFx: forced expiratory flow at 25%, 50%, 75% and 25–75% of forced vital capacity.