The CONTROL statement names variables for sorting the input data set before sample selection. The CONTROL variables can be character or numeric. 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). Ordering the sampling units before systematic or sequential selection can provide additional control over the distribution of the sample.

Control sorting is not available when you use a SAMPLINGUNIT statement, which defines groups of observations as units (clusters) for sample selection. See the description of the SAMPLINGUNIT statement for information about ordering clusters before systematic or sequential selection.

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.