Table 1

Influence of smoking factors on frequency of asthma contacts: univariate analysis

Factor	n	IRR	95% CI	Model χ²	df	p value
Child cotinine level
Low	135	1.00	–
Medium	153	0.91	0.80 to 1.05
High	150	1.19	1.05 to 1.37	17.09	2	0.0002
Amount smoked in home by index parent (cigarettes/day)
0–5	104	1.00	–
6–10	191	0.81	0.71 to 0.92
11–15	78	0.70	0.59 to 0.83
16–20	50	0.74	0.61 to 0.91
>20	15	0.66	0.47 to 0.93	22.63	4	0.0002
Frequency of smoking in room with child
Never	44	1.00	–
Occasionally	118	0.76	0.64 to 0.91
Frequently	48	0.60	0.48 to 0.75
Every day	228	0.66	0.56 to 0.77	28.86	3	<0.000 1
No of parents who smoke
Father only	66	1.00	–
Mother only	194	0.78	0.67 to 0.92
Both parents	178	0.79	0.68 to 0.92	10.73	2	0.005

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).