Table 1

Characteristics of the sample by sex

	Boys		Girls
	No	%	No	%
No of subjects	376		326
Habitual presence in the kitchen
Never	113	30.1	56	17.2
Sometimes	222	59.0	216	66.3
Often	41	10.9	54	16.6
Mean age (years)		13.4		13.2
Father's education (years)
<6	113	30.1	106	32.5
6–8	147	39.1	122	37.4
9–13	101	26.9	72	22.1
>13	15	4.0	21	6.4
Parental smoking	237	63.0	200	61.3
Asthma	40	10.6	12	3.7
Methacholine PC₂₀ ⩽4 mg/ml^1-153	44	12.2	32	10.4
Skin reactors	111	29.7	74	22.8
Geometric mean IgE (IU/ml)		57.0		44.5
FEV₁(l)^1-150		3.11		3.11
FEV₁/FVC (%)^1-150		89%		91%
FEF_25–75 (l/s)^1-150		3.86		4.00
FEF₅₀ (l/s)^1-150		4.24		4.35
FEF₇₅ (l/s)^1-150		2.24		2.45