STRATA Statement

The SURVEYSELECT Procedure

STRATA Statement

STRATA variables ;

You can specify a STRATA statement with PROC SURVEYSELECT to partition the input data set into nonoverlapping groups defined by the STRATA variables. PROC SURVEYSELECT then selects independent samples from these strata, according to the selection method and design parameters specified in the PROC SURVEYSELECT statement. For information on the use of stratification in sample design, refer to Kalton (1983), Kish (1987), and Cochran (1977).

The variables are one or more variables in the input data set. The STRATA variables function much like BY variables, and PROC SURVEYSELECT expects the input data set to be sorted in order of the STRATA variables.

If you specify a CONTROL statement, or if you specify METHOD=PPS, the input data set must be sorted in ascending order of the STRATA variables. So you cannot use the STRATA option NOTSORTED or DESCENDING when you specify a CONTROL statement or METHOD=PPS.

If your input data set is not sorted by the STRATA variables in ascending order, use one of the following alternatives:

Sort the data using the SORT procedure with the STRATA variables in a BY statement.
Specify the option NOTSORTED or DESCENDING in the STRATA statement for the SURVEYSELECT procedure (when you do not specify a CONTROL statement or METHOD=PPS). The NOTSORTED option does not mean that the data are unsorted but rather that the data are arranged in groups (according to values of the STRATA variables) and that these groups are not necessarily in alphabetical or increasing numeric order.
Create an index on the STRATA variables using the DATASETS procedure.

For more information on the BY statement, refer to the discussion in SAS Language Reference: Concepts. For more information on the DATASETS procedure, refer to the discussion in the SAS Procedures Guide.

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