Table 2 Demographic characteristics of subjects included in study by study year

From: Boys with high body masses have an increased risk of developing asthma: findings from the National Longitudinal Survey of Youth (NLSY)

Variable Survey year
  1986 a 1988 1990 1992 1994 1996 1998 2000
N 954b 1754 2336 2954 3473 3678 3904 3166
Mean age in months (range) 11 (0–24) 27 (0–57) 37 (0–80) 49 (0–103) 63 (0–127) 78 (0–150) 96 (0–174) 120 (24–198)
Age (years)
 0–1 95.9 43.2 33.6 23.6 16.4 10.9 7.0 0.0
 2–3 4.1 51.6 31.9 25.7 19.8 15.4 10.5 8.2
 4–5   5.2 30.3 24.6 21.7 17.5 13.5 9.8
 6–7    4.2 23.9 20.0 19.2 16.1 13.7
 8–9     2.2 20.2 17.6 18.4 15.1
 10–1      1.9 18.3 16.2 17.8
 12–13       1.0 17.1 16.1
 14–15        1.0 18.3
 16–17         1.1
Sex         
 Male 50.9 51.6 52.6 51.4 51.4 50.8 50.4 49.7
 Female 49.1 48.4 47.4 48.6 48.6 49.2 49.6 50.3
Race         
 Black 26.4 27.7 29.5 28.1 27.6 27.3 26.9 23.8
 Hispanic 16.6 18.6 20.2 20.1 19.8 19.9 19.8 16.1
 White 57.6 53.6 50.3 51.8 52.6 52.8 53.3 60.2
Poverty         
1 mention 46.2 44.5 41.8 39.8 38.9 38.0 37.8 37.0
 No mention 53.8 55.5 58.2 60.2 61.1 62.0 62.2 63.0
Prenatal maternal smoking         
 Yes 36.3 32.4 28.5 27.8 26.5 24.9 24.5 24.9
 No 62.5 63.8 68.3 68.5 67.0 66.5 66.7 66.5
 Unknown 1.3 3.8 3.2 3.7 6.5 8.6 8.8 8.5
BMI category         
 Missing 0 0.1 1.3 2.1 1.2 1.6 1.3 2.3
 <24 months old 95.9 43.2 33.6 23.6 16.4 10.7 7.0 0.0
 <25th percentile 1.7 18.6 19.1 18.3 31.1 24.8 21.9 15.5
 25th–84th percentile 1.9 24.3 25.9 31.7 30.6 36.5 39.9 44.4
85th percentile 0.5 13.7 20.0 24.4 20.7 26.2 29.8 37.8
 Mean BMI percentile   51 54 59 47 55 58 65
Birth weight         
 <2.5 kg 8.5 7.9 7.0 7.3 7.1 7.0 7.1 6.9
2.5 kg 88.0 85.0 87.4 87.3 84.7 82.9 82.6 83.1
 Unknown 3.6 7.1 5.6 5.4 8.1 10.1 10.3 10.0
Reported asthma at time of survey 0.0 0.1 0.4 1.2 1.2 1.4 2.3 3.0
Incident asthma by 2000 survey 6.5 6.3 6.8 6.5 5.9 5.7 5.4 5.6
  1. From the National Longitudinal Survey of Youth, 1986–2000.
  2. aValues may not add to 100% due to rounding.
  3. bNumbers in this row sum to more than 4393, the total N in the survey, because children were evaluated in multiple years.