Table 1.
Characteristics of the study population.
| Characteristic | All subjects with questionnaire information (n = 3,533) | Subjects with both traffic-related exposures and questionnaire information
|
||
|---|---|---|---|---|
| Total population (n = 2,871) | Cohort population (n = 1,551) | Noncohort population (n = 1,320) | ||
| Sex (percent male) | 50.9 | 51.1 | 50.2 | 52.0 |
| Age [years (mean ± SD)] | 9.36 ± 0.37 | 9.35 ± 0.36 | 9.28 ± 0.35 | 9.45 ± 0.35 |
| Birth weight [kg (mean ± SD)]a | 3.51± 0.55 | 3.50 ± 0.56 | 3.57 ± 0.51 | 3.40 ± 0.61 |
| Furry pets in early life (%) | 18.1 | 18.1 | 19.3 | 16.7 |
| Wall-to-wall carpeting in early life (%) | 31.0 | 32.3 | 31.5 | 33.2 |
| Dampness problems in early life (%)a | 6.3 | 5.7 | 4.7 | 7.0 |
| Parental ethnicity western only (%)b | 75.9 | 79.2 | 92.2 | 63.4 |
| Parental atopy (%) | 57.1 | 59.3 | 64.0 | 53.7 |
| Maternal smoking in pregnancy (%) | 15.5 | 16.1 | 15.3 | 17.2 |
| Maternal education (%) | ||||
| 9–12 years | 28.4 | 29.4 | 28.2 | 31.0 |
| > 12 years | 59.1 | 58.6 | 65.9 | 49.3 |
| Paternal education (%) | ||||
| 9–12 years | 25.0 | 25.5 | 23.3 | 28.1 |
| > 12 years | 60.8 | 60.3 | 66.9 | 52.1 |
| Maternal marital status (%)a | ||||
| Cohabitant | 28.1 | 28.0 | 30.8 | 23.7 |
| Single | 8.8 | 7.6 | 5.5 | 10.5 |
| Cohort indicator (%) | 44.6 | 54.0 | 100 | 0 |
| Skin prick test positivity (%)a | 24.0 | 23.9 | 23.5 | 24.4 |
| Furry pets now (%) | 30.0 | 31.2 | 35.0 | 26.7 |
| Wall-to-wall carpeting now (%) | 13.0 | 13.2 | 10.9 | 16.0 |
| Parental smoking now (%) | 18.1 | 17.8 | 14.0 | 22.3 |
a
Maximum number of subjects with missing data for boys/girls was 395/400 (SPT positivity) and 274/305 (maternal marital status as next covariate after SPT positivity) for the subjects with questionnaire information, 306/306 (SPT positivity), and 135/133 (birth weight as next covariate after SPT positivity) for the subjects with both traffic-related exposures and questionnaire information.
b
Western ethnicity was defined as western Europe, United States, Canada, Australia, or New Zealand as birth country.