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TABLE 1

Baseline Characteristics

Study PopulationExcluded From Analysis
Categorical: n (%); Numeric: Mean (IQR)Missing DataCategorical: n (%); Numeric: Mean (IQR)Missing DataExcluded Compared With the Study Populationa
Children 
Boys (yes or no) 164 (49) 39 (51) .81 
Pregnancy and birth 
Birth wt, kg 3.51 (0.63) 3.52 (0.57) .87 
BMI at birth 12.8 (1.75) 12.8 (1.72) .90 
Caesarean delivery (yes or no) 78 (23) 7 (9) P = .005 
Early exposures 
Older children in household at 1 y (yes or no) 138 (41) 14 (27) 26 .06 
Duration of breastfeeding, mo   16 P = .005 
 0–3 31 (9)  12 (20)   
 3–6 76 (23)  20 (33)   
 ˃6 227 (67)  29 (48)   
Maternal smoking during pregnancy (yes or no) 43 (13) 20 (26) P = .004 
Nicotine level in hair at 1 y (ng/mg) 3.3 (2.1) 14 3.0 (4.4) 29 .73 
Nicotine level in hair at 3 y (ng/mg) 2.0 (0.9) 24 2.2 (0.6) 65 .91 
Day care 
Age at start, d 372 (186) 383 (189) 26 .74 
No. children in day care 29 (41) 12 16.9 (11) 33 P = .002 
Space per child, m2 13 (11) 14 9.7 (6.9) 34 .08 
Indoor environment 
Cat at home at birth (yes or no) 44 (13) 16 (25) 12 P = .02 
Dog at home at birth (yes or no) 49 (15) 5 (8) 12 .13 
Socioeconomic variables 
Household annual income, 100 000 DKR 5.09 (2.4) 3.96 (2.0) 25 P < .001 
Mother’s education   32 .70 
 College or lower level 199 (60)  26 (58)   
 Medium length 89 (27)  11 (25)   
 University 44 (13)  8 (18)   
Mother’s employment 112 (34)  29 .17 
 Nonprofessional 112 (34)  16 (33)   
 Professional 156 (47)  18 (38)   
 Student 37 (12)  5 (10)   
 Unemployed 29 (9)  9 (19)   
Atopic disposition 
Father with asthma 60 (18) 8 (11) .11 
Study PopulationExcluded From Analysis
Categorical: n (%); Numeric: Mean (IQR)Missing DataCategorical: n (%); Numeric: Mean (IQR)Missing DataExcluded Compared With the Study Populationa
Children 
Boys (yes or no) 164 (49) 39 (51) .81 
Pregnancy and birth 
Birth wt, kg 3.51 (0.63) 3.52 (0.57) .87 
BMI at birth 12.8 (1.75) 12.8 (1.72) .90 
Caesarean delivery (yes or no) 78 (23) 7 (9) P = .005 
Early exposures 
Older children in household at 1 y (yes or no) 138 (41) 14 (27) 26 .06 
Duration of breastfeeding, mo   16 P = .005 
 0–3 31 (9)  12 (20)   
 3–6 76 (23)  20 (33)   
 ˃6 227 (67)  29 (48)   
Maternal smoking during pregnancy (yes or no) 43 (13) 20 (26) P = .004 
Nicotine level in hair at 1 y (ng/mg) 3.3 (2.1) 14 3.0 (4.4) 29 .73 
Nicotine level in hair at 3 y (ng/mg) 2.0 (0.9) 24 2.2 (0.6) 65 .91 
Day care 
Age at start, d 372 (186) 383 (189) 26 .74 
No. children in day care 29 (41) 12 16.9 (11) 33 P = .002 
Space per child, m2 13 (11) 14 9.7 (6.9) 34 .08 
Indoor environment 
Cat at home at birth (yes or no) 44 (13) 16 (25) 12 P = .02 
Dog at home at birth (yes or no) 49 (15) 5 (8) 12 .13 
Socioeconomic variables 
Household annual income, 100 000 DKR 5.09 (2.4) 3.96 (2.0) 25 P < .001 
Mother’s education   32 .70 
 College or lower level 199 (60)  26 (58)   
 Medium length 89 (27)  11 (25)   
 University 44 (13)  8 (18)   
Mother’s employment 112 (34)  29 .17 
 Nonprofessional 112 (34)  16 (33)   
 Professional 156 (47)  18 (38)   
 Student 37 (12)  5 (10)   
 Unemployed 29 (9)  9 (19)   
Atopic disposition 
Father with asthma 60 (18) 8 (11) .11 

DKR, Danish kroner.

a

Calculated by χ2 test for categorical risk factors and student’s t test for numerical risk factors.

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