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NHANES Environmental Chemical Data Tutorial

Locate Variables

Purpose

The environmental chemical variables and information about these variables are found in separate data files with accompanying documentation. It is important to read the information in these files and to know how to access them to prepare for your analysis. Use the documentation to decide which environmental chemical variables to include in your analysis, to identify the variable names and their file locations, and to identify the correct sample weights and their file locations. A thorough review of the documentation is an essential part of understanding the environmental chemical variables.

Task 1: Decide Which Environmental Chemical Variables to Include in Your Dataset

Your analysis will require a subset of the environmental chemical variables available from NHANES. To decide which variables are needed for your analysis, review the documentation for each two-year survey cycle of interest.

 

Task 2: Identify Environmental Chemical Variables to Include in Your Dataset

Your analysis will require a subset of the environmental chemical variables available from NHANES. To locate the variables for your analysis, review the documentation for each two-year survey cycle of interest.

 

Task 3: Identify Correct Sample Weights and Their File Locations

Sample weights are constructed for each two-year survey cycle to account for over-sampling, survey non-response, and post-stratification. Because not all persons complete all portions of the survey, each individual in NHANES may be assigned multiple weight variables (see the Survey Orientation Tutorial for more information on how different sample weights are created).  It is important to select the correct weight variables for your particular analysis and take extra care to include it in your analytic dataset.

 

Task 4: Identify Environmental Chemical Laboratory Methods and Corresponding Coefficient of Variation (CV) and Their File Locations

Environmental chemical laboratory methods and corresponding Coefficient of Variation (CV) information are described for each two-year survey cycle and reflect laboratory procedures and the performance of the laboratory method for that survey cycle.   It is important to be familiar with the laboratory methods and any changes that may have occurred over time. Likewise, it is useful to know the variability of the laboratory method as measured by Coefficient of Variation.

 

 

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