### Purpose

Just like continuous NHANES, NHANES I also used a complex, multistage, probability sampling design, and the two surveys share some common features in sample design. Researchers need to take this into account in their analyses by appropriately specifying the sampling design parameters.

This can be done using any statistical software that can analyze complex survey designs. Specifying sampling design parameters using SUDAAN and SAS Survey procedures is presented in this module.

### Task 1: NHANES I Sample Design

NHANES I data were not obtained using a simple random sample. Rather, a complex, multistage, probability sampling design was used to select participants representative of the civilian, non-institutionalized population of the coterminous United States, excluding Indian reservations. Oversampling of certain population subgroups was done to increase the reliability and precision of health status indicator estimates for these groups.

For NHANES I datasets, the use of sampling weights and sample design variables is recommended for all analyses because the sample design is a clustered design and incorporates differential probabilities of selection. If you fail to account for the sampling parameters, you may obtain biased estimates and overstate significance levels.

### Task 2: Specify Sampling Parameters in NHANES I using SUDAAN or SAS Survey Procedures

SUDAAN and SAS Survey are statistical software packages that can be used to analyze complex survey data such as NHANES I.

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