Key Concepts about How the Physical Activity and Cardiovascular Fitness Data Fit into the NHANES Structure
NHANES Survey Cycles
The Continuous NHANES data have been released in 2-year cycles beginning with the NHANES 1999-2000 survey cycle. (Module 4: “Overview of NHANES Survey Design and Weighting” provides more information on the NHANES data cycles.) Some survey topic areas are included in all survey cycles, whereas others are included in selected cycles.
NHANES Data Sections
The data for each NHANES survey cycle are composed of four sections: Demographics, Examination, Laboratory, and Questionnaire. Physical activity and cardiovascular fitness data are found in the Examination and Questionnaire sections.
- Demographics files contain survey design variables including weights, strata and primary sampling units, and demographic characteristics such as sex, age, and race.
- Examination files contain information collected through physical exams (e.g., anthropometric, cardiovascular fitness, and physical activity monitor data).
- Laboratory files contain results from analyses of blood, urine, hair, tuberculin skin test, air, household dust, and water specimens. These files also include glucose, insulin, and blood pressure values, which are commonly used as outcome measures in association studies with physical activity.
- Questionnaire files contain data collected through household interviews, Mobile Examination Center (MEC) interviews, and mailed questionnaires. Physical activity questionnaires are administered through household and MEC interviews but not mailed questionnaires.
Each section contains groups of related variables packaged in one or more data files for each 2-year cycle. This organization scheme allows for efficiency in posting data to and downloading from the NHANES website. Understanding the organization scheme also is helpful for data analyses.
For each cycle of the Continuous NHANES, the Survey Content Brochure1 provides information on data files associated with each section, age ranges for which data on specific variables were collected, and notes describing any additional (non-age-based) exclusions.
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