To choose a cluster sample you divide the population into clusters and then:

1. Cluster sampling saves effort by sampling whole groups. 2. To choose a cluster sample, divide the population into clusters, that is groups. 3. Then randomly select some of the clusters. 4. All members of the selected clusters make up the sample. _Source: OpenStax Introductory Statistics 2e (CC BY 4.0), Ch 1 'Sampling and Data', sections 1.1-1.4_