A cluster sample occurs when you randomly select groups,and for each group selected,you sample every single member of that group.

Cluster Sample

A sampling method where the population is divided into groups, or clusters, and a random sample of these clusters is selected for study.

Randomly Select

The process of choosing items or individuals from a population such that each has an equal chance of being chosen.

Sample

A subset of individuals or observations taken from a larger population for the purpose of statistical analysis.