TABLE I.

Baseline characteristics of participating children according to case-control status^*†

Covariate	Control subjects (n = 327)	Cases (n = 351)
Age (y)	10.5 (2.7)	10.0 (2.6)‡
Female sex	168 (51.4%)	150 (42.7%)‡
Body mass index (z score)	0.5 (1.1)	0.7 (1.2)
Total IgE (IU/mL)§	151.4 (4.7)	295.1 (4.8)‡
Atopy (≥1 positive allergen-specific IgE)	143 (49.8%)	210 (68.9%)‡
Exposure to ETS in utero or before age 2 y	131 (40.2%)	174 (49.6%)‡
Current exposure to ETS	113 (34.6%)	155 (44.2%)‡
Household income <$15,000/y	196 (62.8%)	225 (65.4%)
No parent graduated from high school	64 (19.6%)	63 (18.0%)
No private or employer-based health insurance	205 (62.7%)	239 (68.1%)
Maternal history of asthma	67 (20.8%)	172 (49.3%)‡
Maternal history of asthma, allergic rhinitis, or eczema	86 (26.7%)	190 (54.8%)‡
Low birth weight (<2500 g)	14 (4.5%)	18 (5.2%)
Birth by cesarean section	108 (33.4%)	131 (37.4%)
Prematurity	15 (4.6%)	31 (8.9%)‡
Prematurity requiring NICU admission	6 (1.9%)	21 (6.0%)‡
FEV1 (L)‖	2.0 (0.7)	1.9 (0.7)‡
FEV1/FVC ratio	0.84 (0.1)	0.81 (0.1)‡

^*Data are presented as numbers (percentages) for binary variables or means (SDs) for continuous variables.

^†Percentages were calculated for children with complete data. For example, 592 (287 control subjects and 305 cases) of the 678 participating children had allergen-specific IgE.

^‡P < .05 for the comparisons between groups (performed by using 2-sample t tests or Fisher exact tests, as appropriate).

^§Total IgE transformed to a logarithmic (log₁₀) scale. Results are shown as geometric means (SDs).

^‖FEV₁ values are presented as absolute values because of lack of predicted values for Puerto Rican subjects.