Factor | n | IRR | 95% CI | Model χ2 | df | p value |
Child cotinine level | ||||||
Low | 135 | 1.00 | – | |||
Medium | 153 | 0.98 | 0.84 to 1.14 | |||
High | 150 | 1.15 | 0.99 to 1.34 | 5.49 | 2 | 0.06 |
Amount smoked by index parent (cigarettes/day) | ||||||
<10 | 62 | 1.00 | – | |||
10–19 | 236 | 1.03 | 0.86 to 1.24 | |||
20–29 | 116 | 0.94 | 0.76 to 1.15 | |||
>30 | 24 | 0.99 | 0.72 to 1.35 | 1.61 | 3 | 0.66 |
Amount smoked in the home by index parent (cigarettes/day) | ||||||
0–5 | 104 | 1.00 | – | |||
6–10 | 191 | 1.00 | 0.85 to 1.16 | |||
11–15 | 78 | 0.86 | 0.70 to 1.04 | |||
16–20 | 50 | 0.96 | 0.76 to 1.19 | |||
>20 | 15 | 1.35 | 0.99 to 1.84 | 7.79 | 4 | 0.10 |
Frequency of smoking in room with child | ||||||
Never | 44 | 1.00 | – | |||
Occasionally | 118 | 0.74 | 0.60 to 0.93 | |||
Frequently | 48 | 0.78 | 0.60 to 1.02 | |||
Every day | 228 | 0.92 | 0.75 to 1.12 | 10.61 | 3 | 0.01 |
No of parents who smoke | ||||||
Father only | 66 | 1.00 | – | |||
Mother only | 194 | 1.25 | 1.03 to 1.50 | |||
Both parents | 178 | 1.02 | 0.84 to 1.24 | 10.94 | 2 | 0.004 |
IRR = the incidence rate ratio, the frequency of the number of contacts as a ratio of the frequency in the reference category (the first category of each factor).