Survey Results

Survey Items: The category labeling for childhood obesity has recently changed, due to updates from the CDC. For more information, click here.

Denominator: Children age 10-17 years

Numerator: Underweight (less than 5th percentile); Healthy weight (5th to 84th percentile); Overweight (85th to 94th percentile); Obese (95th percentile or above)

Revisions and Changes: Items K2Q02 and K2Q03 and calculation of BMI-for-age were not changed since 2003. However, changes in CDC's labeling of the 2 highest BMI-for-age categories are reflected in DRC label changes on for the 2007 NSCH. The 85th to 94th percentile range was changed from "At risk of overweight" to "Overweight." The 95th and higher percentile range was changed from "Overweight" to "Obese." For more information, please visit: http://www.cdc.gov/healthyweight/assessing/bmi/childrens_bmi/about_childrens_bmi.html

Additional Notes: Indicator 1.4 is derived directly from the variable BMICLASS in the 2007 NSCH public use data file provided by the National Center for Health Statistics.
Assessment of body fat in children and teenagers is approached differently than for adults. Children's body fat composition changes as they grow, and growth patterns are different for boys and girls. Consequently, measurement of body mass for children, known as BMI-for-age, is age and gender specific.
BMI-for-age categories are: Underweight - Less than the 5th percentile; Healthy weight - 5th percentile to less than the 85th percentile; Overweight - 85th to less than the 95th percentile; Obese - Equal to or greater than the 95th percentile. Additional information about BMI-for-age is available from the CDC online at:
The child's age in months is used to calculate BMI-for-age. However, since the NSCH reports age only in years, all children were assumed to be at the midpoint of their age-year for this calculation.
BMI for children under 10 years of age is not reported in Indicator 1.4. In the NSCH BMI-for-age is based on parents' recollection of the selected child's height and weight. Responses to questions K2Q02 (child's height) and K2Q03 (child's weight) were not independently verified (e.g., measurement, health records, etc.). A study comparing parent-reported height and weight estimates from the 2003 NSCH with results of physical measurement from the National Health and Nutrition Examination Survey (NHANES) revealed that parents typically overestimate height and underestimate weight of children younger than 10 years of age. (Lara J. Akinbami, Cynthia L. Ogden. (2009) Childhood Overweight Prevalence in the United States: The Impact of Parent-reported Height and Weight. Obesity 17:1574-1580)

Treatment of Unknown Values: Unknown values (responses coded as 'refused', 'don't know', or system missing) are not included in the denominator when calculating prevalence estimates and weighted population counts displayed in the data query results table. In nearly every case, the proportion of unknown values is less than 1% and the exclusion of these values does not change the prevalence estimates (%) and only marginally affects the weighted population counts (Weighted Est.). Exceptions are noted in the form of a "Data Alert" at the bottom of a results table.

History and Development: The Maternal and Child Health Bureau leads the development of the NSCH survey and indicators, in collaboration with the National Center for Health Statistics (NCHS) and a national technical expert panel. The expert panel includes representatives from other federal agencies, state Title V leaders, family organizations, and child health researchers. Previously validated questions and scales are used when available. Respondents’ cognitive understanding of the survey questions is assessed during the pretest phase and revisions made as required. All final data components are verified by NCHS and DRC/CAHMI staff prior to public release.