Key Concepts About How the Environmental Chemical Data Fit into the NHANES Data Structure

Cycles

Continuous NHANES data are released in two-year cycles beginning with NHANES 1999-2000 (See the "Overview of NHANES Survey Design and Weights" module for information about the reasons for this policy.)  Some survey topic areas are included in all survey cycles, whereas others are included in selected cycles.

Sections

The data for each survey cycle are composed of four sections:  Demographics, Examination, Laboratory, and Questionnaire. 

• Demographics files contain survey design variables such as weights, strata and primary sampling units, as well as demographic characteristics, such as sex, age, and race.
• Examination files contain information collected through physical exams (including anthropometric and physical activity data), dental exams, and 24-hour dietary recall interviews.)
• Laboratory files contain results from analyses of blood, urine, hair, tuberculin skin test, air, and household dust and water specimens.  These files also include subsample data with unique statistical weights that should be used in analyses of these data.
• Questionnaire files contain data collected through household and Mobile Examination Center (MEC) interviews and mailed questionnaires.

Each section contains groups of related variables, packaged in one or more data files for each two-year cycle.  This organization scheme allows for efficiency in posting data to the website, downloading data, and analyzing data.  Environmental analytes data can be found in the Laboratory section.

For each two-year cycle of continuous NHANES, the 1999-2010 Survey Contents Brochure provides:

• 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.

 

The Survey Contents brochure [PDF - 1.4 MB] ]also lists the different classes of environmental chemicals measured and the years in which they were collected.