Equations | Explained variance for the FEF/FVC equations % | ||||

Reference equation | RSD | Training | Internal validation | External validation | |

Males | |||||

FEF_{25}/FVC s^{−1} | 3.56+0.001A+0.003W−0.013H | 0.286 | 6.79 | 6.48 | 13.16 |

FEF_{50}/FVC s^{−1} | 2.02−0.004A+0.001W–0.006H | 0.205 | 6.17 | 4.76 | 4.04 |

FEF_{75}/FVC s^{−1} | 0.68−0.005A–0.0009W–0.0005H | 0.084 | 35.9 | 32.1 | 37.8 |

FEF_{25–75}/FVC s^{−1} | 1.70−0.007A+0.0005W−0.004H | 0.169 | 16.6 | 13.8 | 14.9 |

Females | |||||

FEF_{25}/FVC s^{−1} | 3.52−0.0005A+0.003W−0.013H | 0.278 | 6.21 | 5.82 | 4.56 |

FEF_{50}/FVC s^{−1} | 2.05−0.005A+0.001W−0.006H | 0.201 | 8.64 | 9.54 | 9.32 |

FEF_{75}/FVC s^{−1} | 0.73−0.006A−0.001W−0.0004H | 0.095 | 41.0 | 41.5 | 46.0 |

FEF_{25–75}/FVC s^{−1} | 1.76−0.008A+0.00009W−0.004H | 0.170 | 23.6 | 24.1 | 25.2 |

FVC: forced vital capacity; RSD: residual standard deviation; FEF_{x}: forced expiratory flow at 25%, 50%, 75% and 25–75% of FVC; A: age (years); W: weight (kg); H: height (cm). Lower limit of normal=value−1.64×RSD; upper limit of normal=value+1.64×RSD.