Supplier
CDC/NCHS
Years Available
From 1960 to 1994, a total of seven periodic cycles of the National Health Examination Survey (NHES) and the National Health and Nutrition Examination Survey (NHANES) were conducted. Beginning in 1999, NHANES has been conducted continuously.
In March 2020, data collection was interrupted due to the coronavirus disease 2019 (COVID-19) pandemic in March 2020. This was the first time survey operations were paused since continuous data collection started in 1999. A new cycle was started in August 2021 using a new sample design that included no oversampling by race and Hispanic origin or income.
In March 2020, data collection was interrupted due to the coronavirus disease 2019 (COVID-19) pandemic in March 2020. This was the first time survey operations were paused since continuous data collection started in 1999. A new cycle was started in August 2021 using a new sample design that included no oversampling by race and Hispanic origin or income.
Periodicity
Continuous since 1999; data are publicly released in 2-year cycles. Estimates are calculated using one or more 2-year cycles. See Methodology section for exceptions.
Mode of Collection
Sample survey: in-home personal interviews, and health examinations and laboratory tests in mobile examination centers (MEC).
Description
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 health 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.
Selected Content
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, and dietary intake. Exams and lab tests provide data on tooth decay and tooth loss, obesity, osteoporosis, high cholesterol, 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.
Population Covered
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.
Methodology
NHANES includes health 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 through March 2020, verified prescription medicine use by examining container labels. Health examinations and laboratory tests follow standardized protocols to ensure comparability across sites and over time. 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 race/Hispanic origin populations) have been oversampled during specific survey cycles. Between 2011-March 2020, the following groups have been oversampled: Hispanic persons; non-Hispanic Black persons; non-Hispanic Asian persons; non-Hispanic White and other persons with family income 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 at or below 130 percent to family income at or below 185 percent of poverty guidelines. The 2017–March 2020 files represent a unique public use data release from NHANES. The partially completed NHANES 2019–2020 cycle was not nationally representative. Therefore, the 2019–March 2020 data were combined with the data from the 2017–2018 cycle to create the nationally representative 2017–March 2020 prepandemic data files.
In previous annual data collection cycles, NHANES selected and screened about 13,000 households to identify, recruit, interview, and examine 5,000 participants. To limit possible SARS-CoV-2 exposure, the August 2021–August 2023 sample design was modified to eliminate oversampling by race, Hispanic origin, and income to reduce the number of households that needed to be screened (to about 7,000) and thereby limiting face-to-face contact between NHANES field staff and the public. While this change reduced the number of households that field interviewers were required to contact, the annual target number of examined participants was maintained at 5,000, and at 10,000 for the full 2-year August 2021–August 2023 cycle. Other design changes included modification of oversampling by age and implementation of multi-mode (self- and interviewer-administered) household screening.
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 – 2020 March, a total of 27,066 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.
For NHANES August 2021 – August 2023, a total of 22,660 persons were eligible to participate in the survey, of which 11,933 (34.5%) were interviewed and 8,860 (25.6%) completed the health examination component.
Interpretation Issues
Data elements, laboratory tests performed, and the methodology of 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 estimates meet the NHANES Analytic Guidelines.
With the discontinuation of oversampling by race and Hispanic origin and income in the August 2021-August 2023 survey, smaller sample sizes for some subgroups (in particular non-Hispanic Black persons and children and adolescents) may result in lower precision and thus lower power to detect differences between groups.
Limitations
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). Due to the COVID-19 pandemic, survey operations were altered. Details of these changes in program and collection procedures can be found in the "Plan and Operations of the National Health and Nutrition Examination Survey, August 2021–August 2023".
Additional documentation of the survey content, data collection procedures, and methods for assessing nonsampling errors is provided elsewhere (National Health and Nutrition Examination Survey | CDC).
References
Terry AL, Chiappa MM, McAllister J, Woodwell DA, Graber JE. Plan and operations of the National Health and Nutrition Examination Survey, August 2021–August 2023. National Center for Health Statistics. Vital Health Stat 1(66). 2024. DOI: https://dx.doi.org/10.15620/cdc/151927
