Methodology and Data Sources

The NHANES at CDC measures obesity rates among Americans ages two and older and is the primary source for national obesity data. NHANES is particularly valuable in that it covers a wide range of people living in the United States, and combines interviews with physical examinations, so includes measured height and weight data. It is conducted every two years.

See NHANES data and trends over time.

These data come from a report of the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) as the result of a biennial census of families served by the program. A strength of these data is that they are a census of all WIC participants and not just a sample of them. The data include height and weight measurements for children, which are collected by medical staff during certification visits, and then are used to calculate BMI and obesity rates among children ages 2 to 4. The data are gathered in April of even-numbered years, and analyzed by the CDC.

See data for children ages 2-4.

NSCH surveys parents of children ages 10 to 17 about all aspects of their children’s health, including height and weight. An advantage of this survey is that it includes both national and state-by-state data, so obesity rates between states can be compared. A disadvantage is that it relies on parent reports, not direct measures. The survey has been conducted annually since 2016, but because the methodology changed in 2016, it is not possible to compare data collected previously with data collected in 2016 or later. In order to increase sample size and enable more reliable state-level estimates, after a large initial sample size in 2016, data are pooled for analyses across two collection years. The Health Resources and Services Administration’s Maternal and Child Health Bureau (HRSA MCHB) funds and directs the NSCH and develops survey content in collaboration with a national technical expert panel and the U.S. Census Bureau, which then conducts the survey on behalf of HRSA MCHB. See data for youth ages 10-17.

YRBSS tracks high-risk health behaviors among students in grades 9-12, including dietary behaviors and physical inactivity. The survey also measures the prevalence of obesity by asking respondents about their height and weight. As in other surveys that use self-reported data to measure obesity rates, this survey likely underreports the true rates. The survey is conducted every two years by the CDC nationally and by state departments of health and education. It is usually conducted during the spring. Results are available for most states, though Minnesota, Oregon, Washington, and Wyoming do not participate and sometimes other states are not able to collect enough responses to adequately report results.

See data for high school students.

Research shows that children who have obesity at an early age are more likely to have obesity later in life, so this site also includes the latest findings from the BRFSS, which tracks state-by-state adult obesity rates. BRFSS is an annual cross-sectional survey designed to measure behavioral risk factors in the adult population (18 years of age or older) living in households. Data are collected from a random sample of adults (one per household) through a telephone survey. The BRFSS currently includes data from 50 states, the District of Columbia, Puerto Rico, Guam and the Virgin Islands. The self-reported height and weight data are then used to calculate obesity rates for each state, territory, and Washington, D.C. A limit of self-reported data is that people tend to over-report their height and under-report their weight, meaning the obesity rates may be underestimates.

See data for adults.