In cluster sampling, clusters are

• A. Individual participants chosen at random
• B. Subsets selected by quotas
• C. Groups of people within the larger population
• D. The same as strata

Answer: (C)

In cluster sampling, the units you sample are groups rather than individuals. These groups, or clusters, are naturally occurring segments of the population—like all students in a school, residents in a neighborhood, or patients at a set of clinics. You randomly pick some of these clusters and collect data from all the individuals within the chosen clusters (or sample within them). This setup distinguishes clusters from individuals chosen at random, and from stratified sampling, where the population is divided into homogeneous strata and sampled from each one. Quota sampling, by contrast, is nonrandom and based on filling predetermined quotas, not on selecting natural groupings. So clusters are groups of people within the larger population.