Table 1.

Characteristics of Subjects by Sex

Characteristic	Male (n = 4,772)		Female (n = 4,849)		P Value*
	n	Percent or Median (IQR)	n	Percent or Median (IQR)
Potential confounders
Lower maternal education†	2,553	59.5	2,567	59.8	0.778
Having ≥1 sibling (parity)	2,331	53.8	2,359	54.5	0.538
Maternal history of asthma or allergy	1,998	47.4	1,971	46.5	0.398
Maternal smoking during pregnancy	985	23.3	957	22.3	0.294
Maternal anxiety during pregnancy‡	1,171	29.8	1,268	32.6	0.009
Low birth weight (<2.5 kg)	193	4.3	208	4.7	0.456
Preterm delivery (<37 wk)	267	5.9	213	4.7	0.010
White ethnic group	4,015	95.6	4,036	95.8	0.684
Ever doctor-diagnosed asthma by age 14 yr	1,164	36.4	931	30.2	2 × 10−7
Day care attendance within first year	272	6.7	253	6.3	0.438
Exposure to smoke from birth to age 8 yr	2,452	64.7	2,505	66.7	0.063
Smoking by 14 yr	454	18.6	966	31.0	2 × 10−16
Smoking by 23 yr	1,753	79.4	2,724	79.6	0.816
Control variables
Childhood spirometry
FEV1 at age 8 yr, L	3,325	1.73 (1.56–1.92)	3,377	1.64 (1.49–1.80)	2 × 10−16
FVC at age 8 yr, L	3,325	1.98 (1.78–2.20)	3,377	1.83 (1.65–2.03)	2 × 10−16
FEV1/FVC at age 8 yr, %	3,325	88.0 (83.2–92.0)	3,377	89.8 (85.8–93.4)	2 × 10−16
FEF25–75% at age 8 yr, L/s	3,325	2.04 (1.67–2.39)	3,377	2.07 (1.74–2.43)	0.001
Variables at 15 yr
Age, yr	2,556	15.3 (15.3–15.5)	2,856	15.4 (15.2–15.6)	7 × 10−4
Height, m	2,535	1.75 (1.70–1.8)	2,807	1.65 (1.61–1.70)	2 × 10−16
Variables at 24 yr
Age, yr	1,358	24.5 (24.0–25.1)	2,169	24.4 (23.8–25.0)	0.001
Height, m	1,355	1.80 (1.75–1.84)	2,151	1.66 (1.62–1.70)	2 × 10−16

Definition of abbreviations: FEF_25–75% = forced expiratory flow, midexpiratory phase; IQR = interquartile range.

^*P value from the χ² or Mann-Whitney test.

^†Educated to the General Certificate of Education level (school-leaving certificate) or lower.

^‡Anxious mothers were defined as being in the fourth quartile of the Crown-Crisp Experiential Index (40).