The National Health and Nutrition Examination Survey (NHANES) is a program of studies designed to assess the health and nutritional status of the U.S.A population by interviewing a nationally representative sample of about 5,000 people across 15 counties each year. The NHANES interviews include demographic, socioeconomic, dietary (including drinking water) and health-related questions. All dietary information is collected with the use of a 24 hour recall, using a computer assisted dietary interview that includes a four step multiple approach. The surveys from 2003 to 2010 are carried out over two days, with Day One consisting of a dietary recall interview which is collected in person in a Mobile Exam clinic (MEC). Day Two involves a dietary recall interview collected over the phone 3-10 days after Day One and is carried out on a different day of the week to the Day One interview. Direct physical measurements are also collected in the MEC.
The participants in the NHANES studies are selected to represent the U.S.A. population of all ages and ethnicities. Participants are selected through a complex statistical process using the most recent Census information. In simple terms, NHANES divides the United States into communities. The communities are then divided into neighbourhoods. The neighbourhoods are selected at random. From each neighbourhood, housing units are selected at random.
Certain subgroups of particular public health interest were over-sampled in the NHANES surveys. This oversampling increased the reliability and precision of estimates of health status indicators for these population subgroups. Weighting schemes allow the estimates from these subgroups to be combined into a national estimate that reflects the relative proportions of these groups in the population as a whole. The procedure to calculate the statistical weight of each participant consists of three steps:
- Computation of weights to compensate for unequal probabilities of selection among subgroups defined by race and Hispanic origin, income, sex, and age.
- Adjustment for non-response; non-respondents may be different from respondents.
- Adjust weighted sample data to match an independent U.S. Census Bureau estimate of the target population totals.
The CARES NG software contains the NHANES data collected in the period 2005-2010 related to those participants who recorded two days of food consumption.
National Health and Nutrition Examination Survey. (2013, April 12). Retrieved 2014, from Centers for Disease Control and Prevention
Curtin, L., Mohadjer, L., & Dohrmann, S. (2013). National Health and Nutrition Examination Survey: Sample design, 2007–2010. National Center for Health Statistics. Vital Health Stat 2(160).
Mirel, L., Mohadjer, L., & Dohrmann, S. (2013). National Health and Nutrition Examination Survey: Estimation Procedures, 2007-2010. National Center for Health Statistics. Vital Health Stat 2(159).
Zipf, G., Chiappa, M., Porter, K., & et al. (2013). National Health and Nutrition Examination Survey: Plan and operations, 1999–2010. National Center for Health Statistics. Vital Health Stat 1(56).
Centers for Disease Control and Prevetion. (2014, January 16). Analytic Note Regarding 2007-2010 Survey Design Changes and Combining Data Across other Survey Cycles. Retrieved 2014, from Centers for Disease Control and Prevention. National Health and Nutrition Examination Survey. Analytic Guidelines