What are the NHANES
environmental chemical data?
The National Health and Nutrition Examination Survey (NHANES) environmental chemical data provide information on environmental exposures based on measures of environmental chemicals or based on metabolites in blood or urine specimens. These data are collected during the laboratory exam in the Mobile Examination Center (MEC) and are used for bio-monitoring of chemical exposures in the United States.
more
NHANES is the only national survey that collects extensive health and nutrition information from face-to-face interviews and medical examinations. The earliest environmental bio-monitoring program began in NHANES II (1976-80), with blood lead tests of all examinees three years of age and older. The bio-monitoring program for environmental chemicals has greatly expanded since then with the current assessment of more than 200 chemicals. The primary goal of the environmental bio-monitoring program is to provide baseline reference data for environmental chemicals. Because it is population-based cross-sectional data, it is best used for descriptive purposes rather than hypothesis testing.
Click to hide
Why was this tutorial created?
NCHS and NCEH developed this web-based tutorial to
meet the growing demands of NHANES environmental chemical data users
and to promote broader and more proficient use of NHANES
environmental chemical data.
more
Whether novice or experienced, all users face
similar challenges when using NHANES environmental
chemical data due to the complexity of the survey design and data
structure. This tutorial was designed so that all users
learn to:
- Efficiently locate pertinent information on
the NCHS website, which is constantly evolving and being
updated;
- Quickly retrieve NHANES environmental chemical data files, a frequent challenge given the complex structure and large amount of data available;
- Correctly prepare an analytic dataset taking into consideration the special issues which may impact the analyses of environmental chemical variables; and
- Correctly conduct statistical analyses that achieve the analyst’s research objectives with appropriate attention paid to the nuances of the data given the complex sample design, weighting requirements, and data structure.
Click to hide
What does the tutorial
provide?
This tutorial walks you through the steps for conducting an analytic project from beginning to end, with examples of common analytic procedures. Relevant environmental chemical data information and nuances, tips and explanations for SAS and SUDAAN programs, downloadable sample program code, and analytic guidance, are organized and integrated into modules and tasks to facilitate this learning process. NHANES primarily assesses exposure to environmental chemical exposures by collecting and testing blood and urine. Therefore, this tutorial will focus its discussion on analytes measured in these types of specimens.
more
The tutorial is intended to be:
- a step-by-step course on environmental chemical data retrieval and analysis for new users;
- a self-learning tool for novice and infrequent users to supplement their knowledge of the NHANES database and the analysis techniques required to properly analyze environmental chemical data in NHANES; and
- a reference for experienced researchers highlighting NHANES' analytic nuances and sample program code.
To best serve the needs of a wide range of users, this tutorial includes a large amount of information. The information is organized in such a way that those who would like to review all information may do so, while others can efficiently bypass sections that are not of interest to them. Overall, this tutorial provides a complete on-line learning tool. Sections of the environmental chemical tutorial may repeat some concepts discussed in other NHANES tutorials, in order to provide a more useful presentation of the environmental chemical analytic topics.
Click to hide
What's the best way to use
the tutorial?
Your own background and learning style will dictate how
you can best use this tutorial.
more
If you are a beginning NHANES
environmental chemical data user, you may want to work
through the tutorial in a linear fashion, starting with the
modules that orient you to the data, then continuing with
the modules about how to prepare an analytic dataset and how
to conduct various types of analyses.
If you are an experienced NHANES data
user and you are searching for specific information or types
of assistance, you can pick and choose other topics of
interest among the modules or even among tasks within
modules.
You are encouraged to use the tutorial's features and
content to suit your own needs, these include:
-
A linear path for users who need step-by-step
self-guided training;
-
Iindex pages and easy navigation throughout
modules that allow you to limit your training to information
on an “as needed” basis;
-
Checklists, summary tables, and animated
demonstrations with audio explanation to enhance learning;
-
Real-life examples to assist you through the
various processes of data preparation and data analysis;
-
Sample code and data files for you to practice
skills and run analyses using your own software;
-
Annotated results with interpretation to help
you troubleshoot your own analyses; and
-
Links to related references and outside
resources.
Click to hide
Who is the audience?
We expect users of this tutorial to come from a broad range of
perspectives and disciplines and to have different levels of
experience with NHANES environmental chemical data and varied degrees
of skill in statistics and software packages.
more
Users will likely fall into one of these groups:
- Public health and other government staff
involved in NHANES environmental chemical data analyses;
- Researchers who use NHANES environmenta chemical data for scientific studies or educational
purposes;
- Public health and medical professionals who
use NHANES environmental chemical data for planning,
policy making, or public health programs; and
- Other users of NHANES environmental chemical data or
groups interested in NHANES.
Click to hide
What key issues may need to be considered when conducting an analysis of NHANES environmental chemical data?
When evaluating the environmental chemical data, some key issues must be kept in mind. These are summarized below.
more
- Issues specific to NHANES environmental chemical data
- NHANES does not test for every environmental chemical that might be of research interest due to factors such as cost, logistic or technical limitations.
- All environmental chemicals measured in NHANES are not measured in all NHANES participants, generally because of cost, participant burden, or other logistic reasons.
- Many of the chemicals are measured only on a subset (for example, of the examined NHANES study sample) thus understanding the sample design and sample weights is crucial (See Module 4 and Module 11).
- Currently, NHANES data can only be used to obtain national estimates and, for confidentality reasons, cannot be used to examine exposure levels by locality, state, or region.
- Currently, NHANES seasonal changes of the year cannot be considered with this NHANES data.
Other issues relevant to NHANES environmental chemical data
- Proximity to sources of exposure cannot be considered with the data.
- Use of particular products cannot be considered with this data.
- Trends over time can only be evaluated when a sufficient number of years of data are available to determine statistically reliable estimates.
- The presence of an environmental chemical does not imply disease or other health effects.
- Levels of environmental substances in blood and urine are not the same as those in air, water, food, soil or dust.
- Having only blood and urine levels measures do not determine which exposure source or which route of exposure has occurred.
- Assessment of persistent substances (with long half lives) might be more meaningful than assessments of non-persistent substances (with short half lives).
Users are encouraged to read further details on NHANES environmental chemical analytic issues in Module 11 of this tutorial.
Click to hide
ShareCompartir 
