Association* of categories of change in severity of obstruction† with shortness of breath while walking at follow-up
| Variable | Crude model | Adjusting for all but asthma covariates‡ | Adjusting for asthma and wheezing at baseline or follow-up | |||
| RR (95% CI) | p Value | RR (95% CI) | p Value | RR (95% CI) | p Value | |
| Incident stage I (n = 683) | 1.59 (1.32 to 1.91) | 0.000 | 1.24 (0.99 to 1.56) | 0.056 | 1.12 (0.89 to 1.41) | 0.344 |
| Incident stage II (n = 85) | 2.74 (1.74 to 4.30) | 0.000 | 1.43 (0.84 to 2.45) | 0.192 | 1.10 (0.63 to 1.90) | 0.743 |
| Persistent stage I (n = 294) | 1.48 (1.13 to 1.94) | 0.004 | 1.14 (0.82 to 1.60) | 0.428 | 1.02 (0.73 to 1.44) | 0.903 |
| Stage I progressing (n = 56) | 3.76 (2.18 to 6.48) | 0.000 | 2.21 (1.10 to 4.45) | 0.026 | 1.71 (0.83 to 3.54) | 0.148 |
| Persistent stage II (n = 61) | 5.43 (3.15 to 9.37) | 0.000 | 4.38 (2.19 to 8.75) | 0.000 | 3.11 (1.50 to 6.42) | 0.002 |
| Non-persistent (n = 113) | 1.02 (0.64 to 1.62) | 0.947 | 1.40 (0.80 to 2.44) | 0.237 | 1.39 (0.80 to 2.43) | 0.246 |
| Asthma at baseline non-current§ | 1.08 (0.70 to 1.65) | 0.739 | ||||
| Asthma at baseline current§ | 0.50 (0.27 to 0.91) | 0.024 | ||||
| Asthma at follow-up non-current§ | 1.09 (0.73 to 1.63) | 0.667 | ||||
| Asthma at follow-up current§ | 2.18 (1.28 to 3.72) | 0.004 | ||||
| Wheezing without a cold at baseline | 1.41 (1.03 to 1.94) | 0.034 | ||||
| Wheezing without a cold at follow-up | 2.07 (1.55 to 2.75) | 0.000 | ||||
↵* Reference category: persistently without obstruction to the airflow.
↵† Obstruction was defined as FEV1/FVC (forced expiratory volume in 1 s/forced vital capacity) <0.70 based on prebronchodilation spirometry.
↵‡ Covariates adjusted for were: sex, age, smoking (light or heavy ever smoker), chronic bronchitis, shortness of breath while walking at baseline, education and area.
↵§ Current asthma was defined as presence of asthma attacks in the 12 months prior to assessment or current asthma medication. Non-current asthma cases were defined as self-declared asthma without attacks or asthma medication.