Multivariate ANCOVA model for siblings
| Contributing factor | Effect ratio* | CI | p Value |
| Intervention group | 0.82 | 0.65 to 1.03 | 0.02 |
| Asthma | 1.04 | 0.82 to 1.31 | 0.74 |
| Parental asthma | 0.89 | 0.73 to 1.08 | 0.25 |
| Sex (male) | 0.84 | 0.66 to 1.07 | 0.16 |
| Māori ethnicity | 1.21 | 0.94 to 1.57 | 0.14 |
| Pacific Island ethnicity | 1.24 | 1.00 to 1.55 | 0.76 |
| Full primary school | 1.05 | 0.78 to 1.41 | 0.88 |
| Intermediate school | 1.21 | 0.84 to 1.74 | 0.31 |
| Secondary school | 1.35 | 0.95 to 1.93 | 0.10 |
| Low income (<$38 000) | 1.08 | 0.82 to 1.42 | 0.60 |
| Smoking inside | 1.49 | 1.13 to 1.96 | 0.006 |
ANCOVA, analysis of covariance.
We have controlled for asthma, since 54% of siblings did not have asthma. Ethnicity was referenced against New Zealand European or other. The level of schooling was referenced against contributing schools (5–10 years). Parental asthma was considered to exist if either parent had ever been diagnosed with asthma. Smoking inside was considered to exist if any level of smoking inside was reported.
↵* The effect ratio is the average number of days absent for those having the specified factor divided by the average number of days absent for those not having the factor after controlling for all other specified factors. Null deviance: 1881.7 on 172 df. Residual deviance: 1241.7 on 160 df. Dispersion factor=7.542391.