From 1960 to 1994, a total of seven national examination surveys were conducted. Beginning in 1999, the survey has been conducted continuously.
Continuous since 1999; data are publicly released in 2-year cycles. Estimates are calculated using one or more 2-year cycles.
Mode of Collection
Sample survey: in-home personal interviews, and physical examinations and laboratory tests in mobile examination centers (MEC).
The National Health and Nutrition Examination Survey (NHANES) is designed to assess the health and nutritional status of adults and children in the United States. The survey is unique in that it combines interviews and physical examinations. The NHANES program includes a series of cross-sectional nationally representative health examination surveys. The health interview includes questions on demographic characteristics, health insurance status, health and diet behaviors, chronic and acute health conditions, mental health, and prescription medication use. Examination components may vary between survey cycles and generally include body measurements (weight, height, skin folds, body composition scans), blood pressure, and dental exams, and may also include vision, hearing, dermatology, fitness, balance and strength testing, respiratory testing, and taste and smell. Laboratory components may include hematology, organ and endocrine function (e.g., thyroid, kidney), environmental exposure, nutrition biomarkers, cardiovascular and metabolic health, and infectious disease.
Data are collected on prevalence of diabetes, cardiovascular disease, kidney disease, and infectious conditions such as hepatitis and human papillomavirus. Health behavior information includes sleep duration, physical activity level, fruit and vegetable intake, and calories from sugar and saturated fat. Exams and lab tests provide data on tooth decay and tooth loss, obesity, osteoporosis, highcholesterol, high blood pressure, hearing loss, nutritional status (e.g. folate,vitamin D), immunization status, and measures of environmental exposures (e.g., lead, secondhand tobacco smoke). Exam and lab tests also provide estimates of the prevalence of undiagnosed conditions.
From 1988 to 1994 (NHANES III), the survey targeted the U.S. civilian noninstitutionalized population aged 2 months and older. Since 1999, all ages are covered.
NHANES includes clinical examinations, selected medical and laboratory tests, and self-reported data. Home interviewers collect and encrypt data on laptops, use printed materials to prompt and verify responses, and verify prescription medicine use by examining container labels. Medical examinations and laboratory tests follow very specific protocols and are standardized to ensure comparability across sites and providers. The sample design is a complex, multistage, clustered design using unequal probabilities of selection. Different groups (e.g., low-income persons, teens, older persons, and selected racial/ethnic populations) have been oversampled during specific survey cycles. Since 2011, the following groups have been oversampled: Hispanic persons; non-Hispanic black persons; non-Hispanic Asian persons; non-Hispanic white and other persons at or below 130 percent of poverty; and non-Hispanic white and other persons ages 80 and older. In 2015-16, the sampling design was revised, changing the cut-point for low-income oversampling from to at or below 185 percent of poverty. The estimation procedure used to produce national statistics for all NHANES involved inflation by the reciprocal of the probability of selection, adjustment for nonresponse, and post stratified ratio adjustment to population totals.
Response Rates and Sample Size
For NHANES 2017-2018, a total of 16,211 persons were eligible to participate in the survey, of which 9,254 (51.9%) were interviewed and 8,704 (48.8%) completed the health examination component.
Data elements, laboratory tests performed, and the methodology of medical examination and laboratory equipment have changed over time. Therefore, trend analyses should carefully examine how specific data elements were collected across the various NHANES surveys. Periodically, NHANES changes its sampling design to oversample different groups. Therefore, trend analyses on demographic subpopulations should be carefully evaluated to determine if the sample sizes meet the NHANES Analytic Guidelines.
Clustered sampling design and limited sample sizes may affect the ability to calculate estimates for select groups (e.g., certain race and Hispanic Origin groups or small age groups).