The National Health and Nutrition Examination Survey (NHANES) is a program designed to assess the health and nutritional status of adults and children in the United States. It combines interviews and physical examinations to gather data. This survey provides a foundation for understanding public health.
Understanding NHANES Data
NHANES collects a wide array of data types, offering a broad scope for public health research. This includes demographic information, such as age, gender, race, ethnicity, and socioeconomic status, which provides context for health trends. Dietary intake data is also collected, detailing food and beverage consumption over a 24-hour period, including specific food items, their sources, and nutrient content.
The survey incorporates detailed physical examinations covering various health measures. These examinations include anthropometric measurements like height, weight, and body composition scans, along with blood pressure readings and dental assessments. Furthermore, laboratory test results from blood, urine, and other tissue samples provide insights into hematology, organ function, environmental exposures, nutritional biomarkers, and infectious diseases. Health questionnaires gather self-reported data on health insurance, behaviors, chronic conditions, mental health, and prescription medication use.
Navigating the Download Process
The official NHANES website, hosted by the Centers for Disease Control and Prevention (CDC), is the primary portal for accessing these datasets. Once on the website, users can find a “Data and Documentation” or similar section to download survey data. The data is organized by survey cycles, with continuous releases occurring every two years since 1999.
Users can select specific survey cycles, such as “NHANES 2019-2020” or “NHANES 2021-2022,” to access the relevant data files. Within each cycle, data is categorized into modules like demographics, dietary, examination, and laboratory data. These data files are commonly available in formats like SAS transport files (.XPT), ASCII, or other statistical software-compatible formats. Accompanying the data files are essential documentation, including detailed codebooks that define variables and their values, as well as copies of the questionnaires used during data collection. Downloading these supplementary materials alongside the data is important for accurate interpretation and use.
Preparing and Analyzing NHANES Data
After downloading the NHANES datasets, proper preparation and analysis are necessary to derive meaningful insights. Common statistical software packages like SAS, R, Python, and SPSS are frequently used for this purpose. These tools are equipped to handle the complexities inherent in NHANES data.
Analyzing NHANES data involves accounting for its complex survey design. The survey employs a multistage, clustered sampling design with unequal probabilities of selection. Therefore, it is important to incorporate survey design features such as weighting, stratification, and clustering into the analysis to ensure accurate and unbiased national estimates.
Each sampled person is assigned a sample weight that reflects the number of individuals they represent in the broader population. These weights adjust for the sampling approach, non-response, and post-stratification to align with U.S. population controls. The codebooks and other documentation are resources for interpreting variables and correctly applying these design features. The data is de-identified to protect the privacy of survey participants.