The SURVEYSELECT Procedure

Unrestricted Random Sampling

The method of unrestricted random sampling (METHOD=URS ) selects units with equal probability and with replacement. Because units are selected with replacement, a unit can be selected for the sample more than once. The expected number of hits (selections) for each unit is $n/N$ when sampling without stratification. For stratified sampling, the expected number of hits for a unit in stratum h is $n_ h/N_ h$. The expected number of hits exceeds one when the sample size n is greater than the population size N.

For unrestricted random sampling, by default, the output data set contains a single copy of each unit selected, even when a unit is selected more than once, and the variable NumberHits records the number of hits (selections) for each unit. If you specify the OUTHITS option, the output data set contains m copies of a sampling unit for which NumberHits is m; for example, the output data set contains three copies of a sampling unit that is selected three times (NumberHits is three). For information about the contents of the output data set, see the section Sample Output Data Set.