| Answered all four questionnaires and blood test (n = 2534)† | Answered all four questionnaires (n = 3619)† | |||||
| Parental smoking | Parental smoking | |||||
| N | n (%) | 95% CI | N | n (%) | 95% CI | |
| Sex | ||||||
| Boy | 1287 | 255 (19.8) | 18.6 to 23.1 | 1822 | 371 (20.6) | 18.5 to 22.2 |
| Girl | 1247 | 260 (20.9) | 17.6 to 22 | 1778 | 367 (20.4) | 18.8 to 22.5 |
| Parental allergy | ||||||
| None | 1746 | 377 (21.6) | 19.7 to 23.5 | 2513 | 955 (21.5) | 19.9 to 23.1 |
| Single | 690 | 125 (18.1) | 15.2 to 21.0 | 955 | 180 (18.8) | 16.4 to 21.3 |
| Double | 78 | 7 (9.0) | 2.4 to 15.5 | 110 | 10 (9.0) | 3.6 to 14.4 |
| Mother’s age | ||||||
| <26 y | 193 | 59 (30.6) | 24.0 to 37.1 | 266 | 74 (27.8) | 22.4 to 33.2 |
| ⩾26 y | 2341 | 456 (19.5) | 17.9 to 21.1 | 3333 | 664 (19.9) | 18.6 to 21.3 |
| Socioeconomic index (SEI)‡ | ||||||
| Blue collar workers | 408 | 139 (34.1) | 29.5 to 38.7 | 626 | 211 (33.7) | 30.0 to 37.4 |
| White collar workers | 2096 | 365 (17.4) | 15.8 to 19.0 | 2964 | 523 (17.6) | 16.3 to 19.0 |
| Exclusive breast feeding | ||||||
| <4 months | 497 | 134 (27.0) | 23.0 to 30.9 | 725 | 188 (25.9) | 22.7 to 29.1 |
| ⩾4 months | 2033 | 380 (18.7) | 17.0 to 20.4 | 2871 | 549 (19.1) | 17.7 to 20.6 |
| Cat ownership | ||||||
| Yes | 253 | 73 (28.9) | 23.2 to 34.4 | 356 | 105 (29.5) | 24.7 to 34.3 |
| No | 2281 | 442 (19.4) | 17.8 to 21.0 | 3244 | 633 (19.5) | 18.1 to 20.9 |
| Dog ownership | ||||||
| Yes | 125 | 41 (32.8) | 24.5 to 41.1 | 187 | 62 (33.1) | 26.3 to 40.0 |
| No | 2409 | 474 (19.7) | 18.1 to 21.3 | 3413 | 676 (19.8) | 18.5 to 21.1 |
N, total number in the group; n, number exposed.
*Mother and/or father smoking at least one cigarette per day when the child was about 2 months old.
†Information available on parental smoking when the child was about 2 months old.
‡Socioeconomic status of the parents according to the socioeconomic index measured by the Nordic Standard Occupational Classification (NYK) and Swedish Socioeconomic Classification (SEI).