Table 1.

Demographic characteristics of the study population.

	Case		Control		Control frequency corrected for sampling
	(N = 193)		(N = 386)		(N = 4312)
Characteristics	N	%	N	%	N ‡	%
Sex
Girls	84	43.5	168	43.5	1876	43.5
Boys	109	56.5	218	56.5	2436	56.5
Parental education, yr†
≦12	116	61.7	264	69.1	2603	60.4
13~15	41	21.8	69	18.1	888	20.6
≧16	31	16.5	49	12.8	821	19.0
Family history of asthma†
No	165	89.2	372	97.9	4212	97.7
Yes	20	10.8	8	2.1	100	2.3
Family history of atopy∗†
No	101	54.6	274	72.1	3252	75.4
Yes	84	45.4	106	27.9	1060	24.6
In utero maternal smoking†
No	189	97.9	382	99.0	4162	96.5
Yes	4	2.1	4	1.0	150	3.5

*Atopy is defined as allergic rhinitis or atopic eczema.

^†Number of subjects does not add up to total N because of missing data.

^‡Predicted number of controls in the TCHS cohort based on the sampling.