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National Health and Nutrition Examination Survey

Description: 

The National Health and Nutrition Examination Survey (NHANES) program includes a series of cross-sectional nationally representative health examination surveys conducted in mobile examination units or clinics. Data are collected on indicators of the nutritional and health status of Americans through dietary intake data, biochemical tests, physical measurements, and clinical assessments for evidence of nutritional deficiencies. Detailed examinations are given by dentists, ophthalmologists, and dermatologists, with an assessment of the need for treatment. Specific components address topics such as cardiorespiratory fitness, physical functioning, lower extremity disease, full body scans for body fat, bone density, and tuberculosis infection.

Data Years Available: 
From 1960-1994, a total of seven national examination surveys were conducted. Beginning in 1999, the survey has been conducted continuously.
Periodicity: 
Continuous since 1999; a minimum of 2 data years is required for analyses.
Mode of Collection: 
In-person interviews in the household or in a private setting in the mobile examination center. Standardized physical examinations and medical tests in mobile examination centers.
Selected Content: 
Data are collected on chronic disease prevalence and conditions (including undiagnosed conditions) and risk factors such as obesity and smoking, serum cholesterol levels, hypertension, diet and nutritional status, immunization status, infectious disease prevalence, health insurance, and measures of environmental exposure. Other topics addressed include hearing, vision, mental health, anemia, diabetes, cardiovascular disease, osteoporosis, oral health, mental health, pharmaceuticals and dietary supplements used, and physical fitness. The National Report on Human Exposures to Environmental Chemicals provides unique exposure information to scientists, physicians, and health officials to help prevent disease that results from exposure to environmental chemicals. Specific public health uses of the exposure information in the National Report series are: - To determine which chemicals get into Americans and at what concentrations; - For chemicals with known toxicity levels, to determine the percent of the population with levels above those associated with adverse health effects; - To establish reverence ranges that can be used by physicians and scientists to determine whether a person has an unusually high exposure; - To assess the effectiveness of public health efforts to reduce exposure of Americans to specific chemicals; - To determine whether exposure levels are higher among minorities, children, women of childbearing age, or other vulnerable groups; To track, over time, trends in levels of exposure of the population; and - To set priorities for research on health effects of exposure.
Population Covered: 
From 1988-94 (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 clinical examinations, selected medical and laboratory tests, and self-reported data. Medical examinations and laboratory tests follow very specific protocols and are as standard as possible to ensure comparability across sites and providers. Beginning in 1999, NHANES became a continuous, annual survey. Data are collected every year from a representative sample of the civilian noninstitutionalized U.S. population, newborns and older, by in-home personal interviews and physical examinations in the mobile examination centers. The sample design is a complex, multistage, clustered design using unequal probabilities of selection. Low-income persons, adolescents 12-19 years of age, persons 60 years of age and over, African Americans, and persons of Mexican origin are oversampled. The sample is not designed to provide nationally representative estimates for the total population of Hispanics residing in the U.S. Sample weights are available and should be used in estimation of descriptive statistics. The complex design features should be used in estimating standard errors for the descriptive statistics.
Response Rates and Sample Size: 
For NHANES 2005-2006, a total of 12,862 persons were identified, of which 80% (10,348) were interviewed and 77% (9,950) completed the health examination component of the survey. For more information on unweighted NHANES response rates and response weights using sample size weighted to Current Population Survey population totals see: {link:10288}.
Interpretation Issues: 
Data elements, laboratory tests performed, and the technological sophistication 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.
References: 

National Center for Health Statistics. Health United States 2009: With Special Feature on Medical Technology. Hyattsville, Maryland. 2010; pp 461-464.