Effect of number of siblings and interbirth interval for children who are the youngest or oldest in the sibship
| Variable | OR (95% CI) for history of asthma | OR (95% CI) for history of hay fever |
|---|---|---|
| For youngest children (n = 2306) | ||
| Number of older siblings 1 | 1.00 (reference) | 1.00 (reference) |
| Number of older siblings ⩾ 2 | 0.82 (0.68, 0.99) | 0.75 (0.60, 0.92) |
| Gap to next sibling | ||
| Interbirth interval 0–2 year4-150 | 1.00 (reference) | 1.00 (reference) |
| Interbirth interval 3–5 years4-150 | 1.09 (0.89, 1.34) | 1.39 (1.10, 1.74) |
| Interbirth interval 6–8 years4-150 | 1.26 (0.71, 2.23) | 1.44 (0.98, 2.11) |
| Interbirth interval ⩾ 9 years4-150 | 1.02 (0.66, 1.56) | 1.45 (0.92, 2.30) |
| Number of residents in 1995 (per one resident increase) (n = 2287) | 0.90 (0.82, 0.99) | 0.84 (0.75, 0.93) |
| For oldest children (n = 1858) | ||
| Number of younger siblings 1 | 1.00 (reference) | 1.00 (reference) |
| Number of younger siblings ⩾ 2 | 0.82 (0.66, 1.02) | 0.84 (0.67, 1.07) |
| Gap to next sibling | ||
| Interbirth interval 0–2 years† | 1.00 (reference) | 1.00 (reference) |
| Interbirth interval 3–5 years† | 0.80 (0.63, 1.00) | 0.92 (0.72, 1.19) |
| Interbirth interval 6–8 years† | 1.02 (0.68, 1.54) | 1.00 (0.64, 1.56) |
| Number of residents in 1995 (per one resident increase) (n = 1845) | 0.80 (0.69, 0.92) | 0.86 (0.75, 1.00) |
↵4-150 Adjusted for number of older siblings; †adjusted for number of younger siblings.