Accounting for the complex sampling design of NHANES I is **critical when
calculating statistical estimates and estimating standard errors** of means,
geometric means, percentages and other statistics. Replication and linearization
are two statistical methods that can be used to properly address these complex
design issues. SAS Survey and SUDAAN use linearization for calculating standard
errors for a variety of statistics, such as means, geometric means and
percentages.

Currently, SUDAAN offers six options for designating survey design (see SUDAAN manual for more details about the use and implications of all design options). SUDAAN assumes a with replacement (WR) design if the design parameter is omitted.

In the next task, you will be using the **with replacement (WR)** design
for analyzing NHANES I data.

In order to implement the WR sampling option in SUDAAN, design variables specifying the first stage of the cluster design and the sample weight are needed.

For more detailed information and sample code, see "Task 2a: How to Use SUDAAN Code to Specify Sampling Parameters in NHANES I."

In SAS, a group of procedures, known as the Survey procedures, produce
estimates from complex sample survey data. These procedures can also produce
variance estimates through linearization (see variance estimation module) and
confidence limits on many estimates. Currently, Taylor Series Linearization is
the only variance estimation method available through SAS Survey procedures. In
the SAS Survey procedure, the sample design is not directly specified in the *
proc* statement, as in SUDAAN, but rather, strata and PSU variables are
specified in separate statements. Similarly, SAS Survey procedure also specifies
the *weight* statement. For more detailed information and sample code, see
"Task 2b: How to Use SAS Survey Code to Specify Sampling Parameters in NHANES
I."

A sample weight is assigned to each sample person. It is a measure of the number of people in the population represented by that sample person in NHANES I, reflecting the unequal probability of selection, nonresponse adjustment, and adjustment to independent population controls. When unequal selection probability is applied, as in the NHANES I sample, the sample weights are used to produce an unbiased national estimate. More information about sample weights and how they are created can be found in the Weighting module.

Unlike in continuous NHANES where masked variance units (MVUs) were used, NHANES I did not create MVUs. Instead, PSEUDO primary sampling units and stratification variables are provided. In NHANES I, 35 pseudo strata and 235 pseudo-PSUs were created for variance estimation for the 1-65 or 1-100 sample (location) design.