Characteristics of the study population and eligible children
| Characteristics at birth | Study population (n=916) | Total eligible population (n=1808) | p Value* |
| Gender (% boys) | 51.2 | 51.1 | 0.89 |
| Region (%) | 0.02 | ||
| North | 32.8 | 30.6 | |
| Middle | 38.3 | 37.7 | |
| West | 28.9 | 31.7 | |
| Study type (%) | 0.02 | ||
| Active intervention | 23.7 | 21.1 | |
| Placebo intervention | 18.0 | 18.8 | |
| Natural history | 58.3 | 60.1 | |
| Allergic mother (%) | 64.7 | 64.9 | 0.90 |
| Allergic father (%) | 30.7 | 31.7 | 0.37 |
| Mother's education (%) | <0.001 | ||
| Low | 18.3 | 22.7 | |
| Medium | 42.6 | 42.1 | |
| High | 39.1 | 35.3 | |
| Father's education (%) | <0.001 | ||
| Low | 20.7 | 25.6 | |
| Medium | 34.3 | 34.1 | |
| High | 45.0 | 40.4 | |
| Mother smoking pregnancy (%) | 9.9 | 16.2 | 0.009 |
| Smoke exposure at home (%) | 18.9 | 22.1 | 0.001 |
| Breast feeding duration (%) | <0.001 | ||
| Never | 14.3 | 20.2 | |
| <3 months | 34.3 | 35.7 | |
| ≥3 months | 51.4 | 44.1 | |
| Gas stove for cooking (%) | 83.7 | 82.9 | 0.33 |
| Older siblings (%) | 48.3 | 48.9 | 0.57 |
| Daycare attendance first year (%) | 24.9 | 23.8 | 0.27 |
| Signs of dampness in the home (%) | 11.5 | 13.1 | 0.03 |
| Cat(s) at home (%) | 29.8 | 29.5 | 0.79 |
| Dog(s) at home (%) | 13.8 | 16.4 | 0.002 |
| Type of home (%) | <0.001 | ||
| Single-family dwelling | 73.4 | 69.7 | |
| Apartment or flat | 26.6 | 30.3 | |
| Fitted carpet (%) | 20.1 | 20.5 | 0.67 |
| Estimated annual average concentrations of (median, interquartile range) | |||
| PM2.5 (μg/m3) | 17.2 (14.7–18.1) | 17.3 (15.0–18.2) | 0.04 |
| Soot (10−5/m) | 1.77 (1.30–1.91) | 1.78 (1.35–1.92) | 0.01 |
| Nitrogen dioxide (μg/m3) | 25.8 (17.4–28.6) | 26.1 (18.7–29.3) | 0.001 |
↵* p Value for difference between study population and eligible children who did not participate.