Transformation of continuous predictors to ordinal predictors
| Predictor | Established categories |
| Patient characteristics | |
| Age years | <55 |
| ≥55 | |
| Age of onset years | <38 |
| ≥38 | |
| BMI kg·m−2 | <22 |
| ≥22 and <36 | |
| ≥36 | |
| Allergy total | No allergy |
| ≥1 allergy | |
| Hyperreactivity | No hyperreactivity |
| ≥1 hyperreactivity | |
| ACQ and CCQ | |
| ACQ1 | 0 or 1 |
| ≥2 | |
| ACQ total, ACQ2, ACQ4, ACQ5, ACQ6 | 0 |
| ≥1 | |
| CCQ subscale mental, CCQ1, CCQ2, CCQ4 | 0 |
| ≥1 | |
| CCQ subscale symptoms, CCQ6 | 0 or 1 |
| ≥2 | |
| CCQ7 | <6 |
| ≥6 | |
| Spirometry results | |
| FEV1 % predicted | <78 |
| ≥78 and <92 | |
| ≥92 and <102 | |
| ≥102 | |
| FVC % predicted | <81 |
| ≥81 | |
| Reversibility % | <7 |
| ≥7 |
Continuous predictors were transformed to ordinal predictors using minimum descriptive length discretisation. It was not possible to create bins for Asthma Control Questionnaire (ACQ) question 3, Clinical COPD Questionnaire (CCQ) questions 3, 5, 8, 9 or 10, CCQ total or CCQ subscale functional, because of low association with the dependent variable. BMI: body mass index; FEV1: forced expiratory volume in 1 s; FVC: forced vital capacity.