Key Concepts About the Data Structure

Cycles

The current NHANES, also known as Continuous NHANES, refers to the two-year cycles of data produced since 1999.

Components

Each cycle is divided into five sections labeled by collection method: Demographics, Dietary, Examination, Laboratory, and Questionnaire.

• Demographics files contain survey design variables such as weights, strata and primary sampling units, as well as, demographic variables.
• Dietary files contain data collected from participants on their dietary intake, which includes, foods, beverages, and dietary supplements.
• Examination files contain information collected through physical exams and dental exams.
• Laboratory files contain results from analyses of blood, urine, hair, air, tuberculosis skin test, and household dust and water specimens.
• Questionnaire files contain data collected through household and mobile examination center interviews.

Component Data Files

Within each section are many components – groups of related variables packaged in a data file. This division allows for efficiency in posting the data files to the website as soon as each component is completed and reviewed and faster download times.

In the picture below, click the years to see how, in Continuous NHANES, a cycle is related to the components and data files. (A screen-reader accessible version of this Flash animation is also available.)