| Characteristic | WATCH | BHS | p Value¶ | ||
| All | Controls | Asthma cases | |||
| Number of participants | 992 | 1323 | 706 | 617 | – |
| Mean (SD) age (years) | 22.4 (15.4) | 53.8 (17.3) | 57.7 (16.0) | 49.5 (17.6) | <0.001* |
| Gender, no (%) | 0.11† | ||||
| Male | 458 (46.2) | 757 (57.2) | 395 (55.9) | 362 (58.7) | |
| Female | 534 (53.8) | 566 (42.8) | 311 (44.1) | 255 (41.3) | |
| Smokers‡, no (%) | 49 (4.9) | 221 (16.7) | 108 (15.3) | 113 (18.3) | <0.001† |
| Mean (SD) BMI | 21.4 (6.0) | 26.1 (4.2) | 26.2 (4.2) | 26.0 (4.2) | <0.001* |
| Asthma, no (%) | 200 (20.2) | 617 (46.6) | 0 (0) | 617 (100) | <0.001† |
| Atopy, no (%) | 482 (48.6) | 1093 (82.6) | 570 (80.7) | 523 (84.8) | <0.001† |
| Eosinophil count (109/l)§ | 0.2 (0.0–0.4) | 0.20 (0.1–0.3) | 0.20 (0.1–0.2) | 0.20 (0.1–0.3) | <0.001* |
| Mean (SD) FEV1 (l) | 2.76 (0.87) | 2.81 (0.98) | 2.82 (0.94) | 2.80 (1.04) | <0.001* |
| Mean (SD) FEV1/FVC ratio | 0.84 (0.08) | 0.75 (0.09) | 0.77 (0.07) | 0.74 (0.10) | <0.001* |
| Dose-response slope§ | – | 2.35 (1.0–6.1) | 1.58 (0.75–3.36) | 4.26 (1.71–25.12) | – |
| IgE (IU/ml)§ | 22.0 (7.0–64.0) | – | – | – | – |
| Exhaled nitric oxide (ppb)§ | 15.1 (8.7–26.2) | – | – | – | – |
*p Value using Mann-Whitney Cox test. †p Value calculated using χ2 test. ‡Considered as a binary outcome. Subjects who were non-smokers or stopped smoking at least 8 months previously were considered to be non-current smokers. Subjects who were current smokers were considered smokers. §Median (interquartile range). ¶p Value for WATCH vs all of BHS.
BMI, body mass index; FEV1, forced expiratory volume in 1 s; FVCD, forced vital capacity.