CDC Obesity Standards

Abstract

Two standards, norm- and criterion-referenced, have often been used to evaluate health outcome measures. The former compare a score with a population and the latter compares the score with a predetermined, absolute, criterion domain behavior (e.g., fit or not fit). Body Mass Index (BMI) has been used as a convenient method of body composition. Derived from 1970s' statistics, the National Center for Health Statistics developed growth charts in 1997 using the percentile curves to indicate the BMI variety by age and gender. A revised version was published in 2000 by the Center for Disease Control and Prevention (CDC) called the CDC Growth Charts, which is now considered the clinical standard to measure the children's growth condition to distinguish the risk of overweight (between 85th and 95th percentiles) and overweight (>95 percentile). Because the percentiles were based on the previous population, they are likely criterion-referenced standards. Purpose Using the data from a new national study, this study was to determine if there was a difference between the CDC percentiles and those of the current child population. Method The data (N = 15,305) of the Early Childhood Longitudinal Study, and the Kindergarten Class (ECLS-K) of 1998–99 were used to compute percentiles by gender (males = 7,807 and females = 7,498), age of 9 (n = 4,008), 9.5 (N=6,557) and 10 (n=3,828) years old, and races (n = 9, e.g., Hispanic, race not specified [Hispanic]; White, non-Hispanic [White]; Black or African American [Black]; Asian) and compared with the CDC percentiles. Results As expected, the BMI values of the current percentiles were higher than their counter-values at the CDC Growth Charts, which is generally consistent across gender, age, race/ethnic groups. Using the BMI values of 9.5-year-old girls (N = 3,272) with selected races as an example: Total Hispanic White Black Asian CDC 5th Percentile 14.30 14.83 14.35 14.34 13.87 13.96 85th Percentile 22.29 22.62 21.91 24.38 20.68 20.18 95th Percentile 26.23 25.91 25.36 29.31 23.65 23.29 Conclusion The obesity standards presented at the CDC Growth Charts are criterion-referenced standards since they were not based on the information of the current children population. The term ttpercentilestt present in the Charts, therefore, was incorrectly used and need to be replaced by a more appropriate criterion-referenced labels (e.g., risks related to obesity) already used in the standards.