The SURVEYSELECT Procedure

When you specify the ALLOC=PROPORTIONAL option in the STRATA statement, PROC SURVEYSELECT allocates the total sample size among the strata in proportion to the stratum sizes, where the stratum size is the number of sampling units in the stratum. The allocation proportion of the total sample size for stratum h is

where is the number of sampling units in stratum h and N is the total number of sampling units for all strata. PROC SURVEYSELECT computes the target sample size for stratum h as

where n is the total sample size that you specify in the SAMPSIZE= option in the PROC SURVEYSELECT statement.

If you specify a minimum stratum sample size in the ALLOCMIN= option in the STRATA statement, then all stratum sample sizes are required to be at least . By default, all stratum sample sizes are required to be at least 1 (to ensure that at least one sampling unit is selected from each stratum). If a target sample size is less than the required minimum value, PROC SURVEYSELECT sets the target sample size equal to the minimum value.

PROC SURVEYSELECT computes the allocated stratum sample sizes (which must be integers) by rounding the target sample size values in order of the fractional parts until the total sample size n is achieved.

PROC SURVEYSELECT provides the target allocation proportions in the output data set variable AllocProportion. The variable ActualProportion contains the actual proportions for the allocated sample sizes . For stratum h, the actual proportion is computed as

where is the allocated sample size for stratum h and n is the total sample size. The actual proportions can differ from the target allocation proportions because of rounding and the requirement that (or ).