Equations | Explained variance for the unadjusted FEF equations % | ||||

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

Males | |||||

FEF_{25} L·s^{−1} | 0.50−0.021A+0.019W+0.040H | 1.478 | 9.73 | 12.1 | 11.6 |

FEF_{50} L·s^{−1} | 0.14−0.038A+0.008W+0.031H | 1.099 | 19.5 | 19.8 | 20.7 |

FEF_{75} L·s^{−1} | 0.14−0.034A−0.005W+0.018H | 0.469 | 46.8 | 44.7 | 55.0 |

FEF_{25–75} L·s^{−1} | 0.37−0.048A+0.003W+0.029H | 0.903 | 32.6 | 31.9 | 39.2 |

Females | |||||

FEF_{25} L·s^{−1} | 1.21−0.026A+0.015W+0.029H | 1.039 | 15.6 | 17.0 | 15.4 |

FEF_{50} L·s^{−1} | 0.51−0.033A+0.007W+0.024H | 0.778 | 27.1 | 27.7 | 29.8 |

FEF_{75} L·s^{−1} | 0.35−0.028A−0.005W+0.014H | 0.375 | 51.4 | 52.0 | 56.8 |

FEF_{25–75} L·s^{−1} | 0.74−0.041A+0.0015W+0.023H | 0.654 | 42.3 | 42.6 | 44.1 |

RSD: residual standard deviation; FEF_{x}: forced expiratory flow at 25%, 50%, 75% and 25–75% of forced vital capacity; 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.