Descriptive statistics of life-course factors in the study sample
| Cohort member characteristics | Total (n=6212) | No parental respiratory disease history (n=5983) | Reported parental respiratory disease history (n=229) | p-value# |
| Smoking exposure | ||||
| Childhood passive smoke exposure | 4185 (67%) | 4015 (67%) | 170 (74%) | 0.024 |
| Adulthood passive smoke exposure | 3470 (56%) | 3330 (56%) | 140 (61%) | 0.101 |
| Adulthood smoking status | 0.003 | |||
| Never | 3751 (60%) | 3620 (61%) | 131 (57%) | |
| Ever | 1330 (21%) | 1292 (22%) | 38 (17%) | |
| Persistent | 1131 (18%) | 1071 (18%) | 60 (26%) | |
| Cumulative smoking | 0.002 | |||
| 0 (never) | 905 (15%) | 885 (15%) | 20 (9%) | |
| 1 | 1874 (30%) | 1802 (30%) | 72 (31%) | |
| 2 | 1702 (27%) | 1645 (28%) | 57 (25%) | |
| 3 | 1031 (17%) | 993 (17%) | 38 (17%) | |
| 4 (persistent exposure) | 700 (12%) | 658 (11%) | 42 (18%) | |
| SC | ||||
| At birth | 0.001 | |||
| SC1 | 1216 (20%) | 1191 (20%) | 25 (11%) | |
| SC2 | 619 (10%) | 604 (10%) | 15 (7%) | |
| SC3 | 3096 (50%) | 2962 (50%) | 134 (59%) | |
| SC4 | 1281 (21%) | 1226 (20%) | 55 (24%) | |
| At 11 years of age | <0.001 | |||
| SC1 | 1570 (25%) | 1544 (26%) | 26 (11%) | |
| SC2 | 670 (11%) | 650 (11%) | 20 (9%) | |
| SC3 | 2640 (43%) | 2550 (43%) | 90 (39%) | |
| SC4 | 1332 (22%) | 1239 (21%) | 93 (41%) | |
| At 42 years of age | 0.001 | |||
| SC1 | 2535 (41%) | 2459 (41%) | 76 (33%) | |
| SC2 | 1512 (24%) | 1465 (25%) | 47 (21%) | |
| SC3 | 1179 (19%) | 1127 (19%) | 52 (22%) | |
| SC4 | 986 (16%) | 932 (16%) | 54 (24%) | |
| Cumulative SC mean±sd (range 0–9) | 4.42±2.43 | 4.38±2.42 | 5.41±2.29 | <0.001 |
| Asthma | ||||
| Childhood asthma | 1391 (22%) | 1328 (22%) | 63 (28%) | 0.058 |
| Adulthood asthma | 818 (13%) | 766 (13%) | 52 (23%) | <0.001 |
| Cumulative asthma | 0.003 | |||
| 0 (never) | 4430 (71%) | 4290 (72%) | 140 (61%) | |
| 1 | 1361 (22%) | 1298 (22%) | 63 (28%) | |
| 2 (persistent) | 421 (7%) | 395 (7%) | 26 (11%) | |
| Others | ||||
| Low birth weight | 317 (5%) | 293 (5%) | 24 (111%) | <0.001 |
| Born preterm¶ | 216 (4%) | 209 (4%) | 7 (3%) | 0.723 |
| Had pneumonia¶ | 266 (4%) | 251 (4%) | 15 (7%) | 0.084 |
| Biomass exposure¶ | 776 (13%) | 742 (12%) | 34 (15%) | 0.272 |
| Occupational exposure | 1897(31%) | 1813 (30%) | 84 (37%) | 0.040 |
SC: social class (SC1: professional/managerial; SC2: unskilled nonmanual; SC3: skilled manual; SC4: unskilled manual). #: calculated by Chi-squared or independent sample t-test as appropriate, significant level set at p<0.1; ¶: based on mean of 10 imputed datasets.