A cluster sample is a probability sample distinguished by a two-step procedure in which
- the parent population is divided into mutually exclusive and exhaustive subsets, and
- 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.
- ^ American Marketing Association, AMA Dictionary.