Table 4

Influence of smoking factors on frequency of non-respiratory contacts: univariate analysis

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).