Table 2.

Association between environmental exposures during the first 2 years of life and variation in asthma age-of-onset

Environmental variable	Sample size	t-Statistic	P-value
			Uncorrected	Correcteda
Type of house (brick or wood)	977	4.233	2.5 × 10−5	1 × 10−4
Carpet exposure	1002	5.152	6.2 × 10−5	5 × 10−4
Serious chest illness	1001	3.833	1.4 × 10−4	0.0016
Direct exposure to father's smoking	377	−4.148	2.6 × 10−4	0.0033
Father a cigarette smoker	1050	−3.430	6.3 × 10−4	0.0103
Breastfeeding as an infant (under 6 months of age)	348	2.196	0.0287	0.3878
Location of house (major city/town or rural area)	1077	1.935	0.0533	0.5978
Otitis media	353	1.433	0.1526	1
Duration of breastfeeding	287	−1.285	0.1997	1
Dog exposure	1065	−1.204	0.2290	1
House less than 50 m from a main road	1027	−1.048	0.2950	1
Quantity of cigarettes smoked daily by mother	58	0.863	0.3119	1
Direct exposure to mother's smoking	388	−0.762	0.4460	1
Cat exposure	1063	−0.758	0.4490	1
Mother a cigarette smoker during pregnancy	390	−0.552	0.5810	1
Quantity of cigarettes smoked daily by father	137	−0.156	0.8761	1
Mother a cigarette smoker	1060	0.138	0.8900	1

^aP-value is corrected for multiple testing by 10,000 permutations.

Statistically significant associations (P < 0.05) after correction for multiple testing are displayed in bold.