Survey sampling is the process of selecting a probability-based sample from a finite population according to a sample design. You then collect data from these selected units and use them to estimate characteristics of the entire population.

A sample design encompasses the rules and operations by which you select sampling units from the population and the computation of sample statistics, which are estimates of the population values of interest. The objective of your survey often determines appropriate sample designs and valid data collection methodology. A complex sample design can include stratification, clustering, multiple stages of selection, and unequal weighting. The survey procedures can be used for single-stage designs or for multistage designs, with or without stratification, and with or without unequal weighting.

To analyze your survey data with the SURVEYMEANS, SURVEYFREQ, SURVEYREG, SURVEYLOGISTIC, and SURVEYPHREG procedures, you need to specify sample design information for the procedures. This information can include design strata, clusters, and sampling weights. All the survey analysis procedures use the same syntax for specifying sample design information. You provide sample design information with the STRATA, CLUSTER, and WEIGHT statements, and with the RATE= or TOTAL= option in the PROC statement.

If you provide replicate weights for BRR or jackknife variance estimation, you do not need to specify a STRATA or CLUSTER statement. Otherwise, you should specify STRATA and CLUSTER statements whenever your design includes stratification and clustering.

When there are clusters (PSUs) in the sample design, the procedures estimate variance by using the PSUs, as described in the section Variance Estimation. For a multistage sample design, the procedures use only the first stage of the sample design for variance estimation. Therefore, the required input includes only first-stage cluster (PSU) and first-stage stratum identification. You do not need to input design information about any additional stages of sampling.

The following sections provide brief descriptions of basic sample design concepts and terminology used in the survey procedures. For more detailed information, see Lohr (2010); Kalton (1983); Cochran (1977); Kish (1965).