When an equal-probability sample is selected in PROC SURVEYSELECT and a STRATA statement is specified, unequal selection probabilities might be used. When this happens, the resulting sample is incorrect. This problem can occur when the METHOD= option is omitted or if any of the following METHOD= options are specified in the PROC SURVEYSELECT statement:
To circumvent this problem, specify the RANUNI option in the PROC SURVEYSELECT statement.