Table 1 Stepwise exclusion of subjects with respiratory diseases, symptoms and smoking history: mean (SD) FEV1, FVC and FEV1/FVC at each step.
| n | FEV1 | FVC | FEV1/FVC | |
|---|---|---|---|---|
| Parent population (A) | 2358 | 3.22 (0.94) | 4.09 (1.14) | 0.785 (0.067) |
| Subjects without cardinal symptoms (B), standardised† | 1184 | 3.35 (0.42) | 4.21 (0.53) | 0.796 (0.096) |
| Stepwise exclusion from population type A to type B | ||||
| Not obstructive lung diseases in 1996 | 2188 | 3.28 (0.91)* | 4.15 (1.12)* | 0.790 (0.059)* |
| Not breathlessness grade 4 | 2148 | 3.29 (0.91)* | 4.16 (1.12)* | 0.790 (0.059)* |
| Not breathlessness grade 3 | 2099 | 3.31 (0.90)* | 4.18 (1.11)* | 0.790 (0.058)* |
| Not breathlessness grade 2 | 1886 | 3.36 (0.88)* | 4.25 (1.09)* | 0.791 (0.057)* |
| Not morning cough | 1498 | 3.41 (0.89)* | 4.29 (1.11)* | 0.795 (0.054)* |
| Not breathlessness grade 1 | 1377 | 3.44 (0.88)* | 4.33 (1.10)* | 0.796 (0.054) |
| Not wheeze | 1205 | 3.43 (0.88) | 4.31 (1.09)* | 0.797 (0.053)* |
| Not chronic cough | 1184 | 3.44 (0.88)* | 4.32 (1.09)* | 0.797 (0.053) |
| Never‐smokers without cardinal symptoms (C), standardised† | 539 | 3.39 (0.42) | 4.25 (0.53) | 0.799 (0.096) |
| Stepwise exclusion from population type B to type C | ||||
| Never‐smokers | 539 | 3.43 (0.94) | 4.28 (1.18) | 0.801 (0.051)* |
| Never‐smokers without any symptoms (D), standardised† | 331 | 3.40 (0.42) | 4.25 (0.53) | 0.799 (0.096) |
| Stepwise exclusion from population type C to type D | ||||
| Not phlegm | 501 | 3.43 (0.94) | 4.29 (1.17) | 0.801 (0.051) |
| Not attacks of breathlessness | 484 | 3.43 (0.93) | 4.30 (1.17) | 0.801 (0.052) |
| Not day cough | 477 | 3.44 (0.93) | 4.30 (1.16) | 0.801 (0.051) |
| Not infancy lung disease | 471 | 3.44 (0.93) | 4.30 (1.16) | 0.801 (0.051) |
| Not cough with cold | 335 | 3.40 (0.95) | 4.25 (1.18) | 0.800 (0.053) |
| Not woken by breathlessness | 332 | 3.40 (0.95) | 4.26 (1.19) | 0.800 (0.053) |
| Not breathlessness and wheeze | 331 | 3.40 (0.95) | 4.26 (1.19) | 0.799 (0.053) |
FEV1, forced expiratory volume in 1 s; FVC, forced vital capacity.
*p⩽0.05 between analysed group and those excluded since previous analysis.
†Lung function estimates were standardised for the distribution of sex, age and height in the parent population. Estimates not marked with † are non‐standardised.