Cluster sample

A probability sample distinguished by a two-step procedure in which (1) the parent population is divided into mutually exclusive and exhaustive subsets, and (2) a random sample of subsets is selected. If the investigator then uses all of the population elements in the selected subsets for the sample, the procedure is one-stage cluster sampling; if a sample of elements is selected probabilistically from the subsets, the procedure is two-stage cluster sampling.