The CONTROL statement names variables for sorting the input data set. The CONTROL variables can be character or numeric.

PROC SURVEYSELECT sorts the input data set by the CONTROL variables before selecting the sample. If you also specify a STRATA statement, PROC SURVEYSELECT sorts by CONTROL variables within strata. Control sorting is available for systematic and sequential selection methods (METHOD=SYS, METHOD=PPS_SYS, METHOD=SEQ, and METHOD=PPS_SEQ).

By default (or if you specify the SORT=SERP option), PROC SURVEYSELECT uses hierarchic serpentine sorting by the CONTROL variables. If you specify the SORT=NEST option, the procedure uses nested sorting. For more information about serpentine and nested sorting, see the section Sorting by CONTROL Variables.

You can use the OUTSORT= option to name an output data set that contains the sorted input data set. If you do not specify the OUTSORT= option when you use the CONTROL statement, then the sorted data set replaces the input data set.