Survey Results

Survey Items: The CDC established the categories for reporting BMI and age related data from youth 17 and under. 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: Same as the 2007 and 2003 NSCH; may compare across survey years with special attention to the addition of cell phones in the 2011/12 NSCH sample.

Additional Notes: Indicator 1.4 is derived directly from the variable BMICLASS in the 201/12 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. The samples in 2003 and 2007 were drawn by random digit dial telephone sampling. The 2011/12 survey included the addition of cell phones to the sample. This has implications for the comparability of items between 2007 and 2011/12. More information can be found in the “Learn About the Surveys” section of this website.