OR | 95% CI | p-value | |

Age years | 1.04 | 0.97–1.11 | 0.309 |

Males | 1.30 | 0.30–1.99 | 0.590 |

BMI <18.5 kg·m^{−2} | 3.51 | 1.38–8.93 | 0.008 |

Received long-term oxygen therapy | 1.58 | 0.30–8.19 | 0.586 |

P_{O2}kPa | 0.87 | 0.59–1.29 | 0.481 |

P_{CO2}kPa | 0.80 | 0.39–1.69 | 0.555 |

FEV_{1} L | 0.16 | 0.21–1.17 | 0.071 |

FVC L | 0.33 | 0.16–0.68 | 0.003 |

TLC L | 0.99 | 0.96–1.01 | 0.325 |

RV % pred | 0.99 | 0.99–1.01 | 0.895 |

RV/TLC ratio % pred | 1.07 | 1.01–1.13 | 0.026 |

T_{LCO}(<20%) | 13.22 | 3.07–56.9 | 0.001 |

T_{LCO}(20–39%) | 2.89 | 0.77–10.9 | 0.116 |

Significant variables are shown in bold. Odds ratios are per unit increase for continuous variables. For categorical variables, the group for which the odds ratio is shown is described. BMI: body mass index; *P*_{O2}: partial pressure of oxygen; *P*_{CO2}: partial pressure of carbon dioxide; FEV_{1}: forced expiratory volume in 1 s; FVC: forced vital capacity; TLC: total lung capacity; RV: residual volume; % pred: % predicted; *T*_{LCO}: transfer factor of the lung for carbon monoxide.