# Environmental Chemical Data Analyses

- Module 14: Estimating variance, analyzing subgroups and calculating degrees of freedom for performing statistical tests and calculating confidence intervals
- Module 15: Assess normality and estimate percentiles, geometric means, and proportions
- Module 16: Testing hypotheses

These courses are the same as those presented in the Continuous NHANES tutorial, although in Module 15, the sample computer programs and output are based on environmental data sets created earlier in this tutorial. It is recommended that analysts review Modules 11–13 in the course “Critical Issues of Analysis of Environmental Chemical Data” in order to understand key aspects to consider when analyzing these data. The key aspects include:

- Adjustments for lipids and creatinine;
- Limits of Detection;
- Subsample sizes;
- Laboratory procedure changes;
- Data release changes;
- Routes of exposure;
- Cross sectional nature of NHANES; and
- Other changes across NHANES cycles.

For issues related to specific analytic topics please see the corresponding section in the Continuous NHANES Web Tutorial and the SAS program, which can be downloaded from the Continuous NHANES Web Tutorial.

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- cdcinfo@cdc.gov