Key Concepts About How the Environmental Chemical Data Fit into the NHANES
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
The data for each survey cycle are composed of four
sections: Demographics, Examination, Laboratory, and
- 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
- Questionnaire files contain
data collected through household and Mobile Examination Center (MEC) interviews and
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
For each two-year cycle of continuous NHANES, the 1999-2010
Survey Contents Brochure provides:
- Data files associated with each
- Age ranges for which data on
specific variables were collected; and
- Notes describing any additional
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.