Characteristics of those attending and not attending the laboratory study (of a total of 1397 who were invited to attend)
| Characteristic | Attended laboratory (n=837) | Did not attend laboratory (n=560) | p-value |
| Age# years | 44.83±0.996 | 44.79±0.934 | 0.39 |
| Sex | |||
| Male | 412 (49.2) | 297 (53.0) | |
| Female | 425 (50.8) | 263 (47.0) | 0.16 |
| BMI kg·m−2 | 28.19 (5.93) | 28.85 (6.82) | 0.06 |
| Smoking status | |||
| Never | 367 (44.2) | 215 (38.9) | |
| Former | 258 (31.2) | 152 (27.5) | |
| Current | 204 (24.6) | 186 (33.6) | 0.001 |
| Asthma | |||
| Never | 265 (31.9) | 205 (36.9) | |
| Remitted | 298 (35.9) | 188 (33.8) | |
| Current | 268 (32.2) | 163 (29.3) | 0.15 |
| Social class | |||
| Level 1 | 262 (31.7) | 134 (24.3) | |
| Level 2 | 103 (12.4) | 63 (11.5) | |
| Level 3 | 171 (20.7) | 106 (19.2) | |
| Level 4 | 143 (17.3) | 107 (19.5) | |
| Level 5 (lowest) | 148 (17.9) | 140 (25.5) | 0.002 |
| Atopy | |||
| No | 345 (41.9) | 268 (48.7) | |
| Yes | 478 (58.1) | 282 (51.3) | 0.013 |
| Family history of asthma | |||
| Neither parent | 589 (74.5) | 400 (76.9) | |
| One or both parents | 202 (25.5) | 120 (23.1) | 0.17 |
Data are presented as mean±sd or n (%), unless otherwise stated. BMI: body mass index. #: At the 2006 laboratory study.