TABLE 1.
CHARACTERISTICS OF THE STUDY POPULATION
| N | % | N Total | |
|---|---|---|---|
| Child characteristics | |||
| Sex, male | 2,908 | 50.7% | 5,738 |
| Birth weight, g, median, percentiles 25, 75 | 3,450 | 3,120, 3,770 | 5,670 |
| Body mass index at 7 yr, kg, median, percentiles 25, 75 | 15.8 | 14.9, 17.0 | 5,693 |
| Environmental exposures | |||
| Any older brothers at age 1.5 yr | 3,197 | 55.7% | 5,738 |
| Weekly contact with pets at age 2 or 4.5 yr* | 4,585 | 82.5% | 5,555 |
| Exposure to environmental tobacco smoke at 6 mo† | 1,676 | 29.8% | 5,620 |
| TV watching at 5.4 yr, > 2 h during weekdays | 506 | 9.5% | 5,348 |
| Maternal characteristics | |||
| Age at delivery, yr, median, percentiles 25, 75 | 29 | 26, 32 | 5,738 |
| Higher education‡ | 2,498 | 44.3% | 5,638 |
| Social class I, II | 2,110 | 42.9% | 4,923 |
| Asthma | 651 | 11.7% | 5,564 |
| Allergy | 2,577 | 46.4% | 5,548 |
| Hay fever | 1,750 | 31.8% | 5,498 |
| Clinical evaluation at 7–8 yr | |||
| Positive skin prick test | 1,226 | 21.4% | 5,738 |
| Lung function | Median | Percentiles 25, 75 | N |
| Standard deviation scores adjusted for height, age, and sex | |||
| FVC | −0.01 | −0.62, 0.66 | 4,708 |
| FEV1 | 0.01 | −0.65, 0.66 | 4,636 |
| FEV1:FVC ratio | 0.89 | 0.85, 0.93 | 4,636 |
| Forced midexpiratory flow (FEF25–75) | −0.04 | −0.68, 0.64 | 4,708 |
| Bronchial hyperresponsiveness§ | 0.10 | −1.33, 1.05 | 3,117 |
N = 5,738.
*
Cat, dog, or any furry pet.
†
During the weekend.
‡
Maternal higher education: a level or degree (studying at least until age 18 yr).
§
Mean of least squares dose–response slope. Percentage decline in FEV1 per μmol methacholine.