The code needed to calculate variance estimates using SAS Survey procedures is described below. In this example, the SAS Survey procedure, proc surveymeans, is used and the name of the dataset is BP_analysis_Data. Proc surveymeans is being used as a generic example, but the strata, cluster, and weight statements apply to all SAS Survey procedures.
The strata statement names the variables that form the strata. For the Continuous NHANES, the variable that identifies the sample strata is named sdmvstra.
The cluster statement names the variables that identify the clusters in a clustered sample design such as NHANES. Clusters are nested within the strata.
In NHANES, the variable that represents the sample clusters is named sdmvpsu (masked PSUs).
The following table shows how to combine the statements described above to properly specify the sample design parameters using SAS Survey procedures. In this example, the proc surveymeans procedure is used to calculate variance. However, the strata and cluster statements can be used in a similar manner for all SAS Survey procedures. The steps in this task identify the most basic statements used in SAS Survey procedures to account for the complex sample design of NHANES. Additional procedure options can be added to these statements to customize the variance estimates, statistics, and the output from your procedure to suit individual analytic needs. Please consult the SAS/STAT manual for specifications on the options for each SAS Survey procedure.
Statements | Explanation |
---|---|
data= BP_analysis_Data; | Use the SAS Survey procedure, proc surveymeans, to calculate means and standard errors, and specify the dataset (BP_analysis_Data). |
stratum sdmvstra; | Use the stratum statement to specify the strata (sdmvstra) — this accounts for the design effects of stratification. |
cluster sdmvpsu; | Use the cluster statement to specify primary sampling unit (sdmvpsu) — this accounts for the design effects of clustering. |
Reference: SAS Institute Inc., SAS/STAT User's Guide, Version 9.1; see: Survey Means Procedure