Table 4 Number of girls developing asthma, person-years of follow-up, and incidence rate of asthma, stratified by baseline body mass index (BMI) categories and aggregated BMI categories over the first two, first three and first four surveys From the National Longitudinal Survey of Youth, 1986–2000.

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

Variable N Percent a Number developing asthma Person-years at risk Incidence rate (per 1000 person years)
BMI category at baseline (age 2–3 years old)      
 <25th percentile 684 31.5 25 4261 5.9
 25th–84th percentile 797 36.6 39 5008 7.8
85th percentile 694 31.9 25 3748 6.7
 Total 2175   89 13017 6.8
BMI categories for first two surveysb (age 4–5 years old)      
 Always <25th percentile 229 15.1 6 1281 4.7
 Others 599 39.4 19 3634 5.2
 Always 85th percentile 171 11.2 9 941 9.6
 1 time 85th percentile 521 34.3 24 3012 8.0
 Total 1520   58 8867 6.5
BMI categories for first three surveysc (age 6–7 years old)      
 Always <25th percentile 92 7.6 3 413 7.3
 Others 474 39.3 12 2277 5.4
 Always 85th percentile 75 6.2 5 349 14.3
 1or 2 times 85th percentile 564 46.8 22 2703 8.1
 Total 1205   42 5742 7.3
BMI categories for first four surveysd (age 8–9 years old)      
 Always <25th percentile 40 4.7 0 151 0
 Others 285 33.3 8 1159 6.9
 Always 85th percentile 40 4.7 1 165 6.1
 1–3 times 85th percentile 490 57.3 16 1854 8.6
 Total 855   25 3329 7.5
  1. aValues may not add to 100% due to rounding.
  2. bLimited to girls who were asthma-free at first and second surveys.
  3. cLimited to girls who were asthma-free at first, second, and third surveys.
  4. dLimited to girls who were asthma-free at first, second, third, and fourth surveys.