Sampling Wizard: Design Variables
This step allows you to select stratification and clustering variables and to define input sample weights. You can also specify a label for the stage.
Stratify By. The cross-classification of stratification variables defines distinct subpopulations, or strata. Separate samples are obtained for each stratum. To improve the precision of your estimates, units within strata should be as homogeneous as possible for the characteristics of interest.
Clusters. Cluster variables define groups of observational units, or clusters. Clusters are useful when directly sampling observational units from the population is expensive or impossible; instead, you can sample clusters from the population and then sample observational units from the selected clusters. However, the use of clusters can introduce correlations among sampling units, resulting in a loss of precision. To minimize this effect, units within clusters should be as heterogeneous as possible for the characteristics of interest. You must define at least one cluster variable in order to plan a multistage design. Clusters are also necessary in the use of several different sampling methods. See the topic Sampling Wizard: Sampling Method for more information.
Input Sample Weight. If the current sample design is part of a larger sample design, you may have sample weights from a previous stage of the larger design. You can specify a numeric variable containing these weights in the first stage of the current design. Sample weights are computed automatically for subsequent stages of the current design.
Stage Label. You can specify an optional string label for each stage. This is used in the output to help identify stagewise information.
Note: The source variable list has the same content across steps of the Wizard. In other words, variables removed from the source list in a particular step are removed from the list in all steps. Variables returned to the source list appear in the list in all steps.