Cluster Sampling

Cluster Sampling is a sampling strategy (a way to gather participants for a study) used when it is difficult to individually identify every person in a sample, and naturally-occurring groups are available.

Let's say you want to conduct a study involving nurses in the United States. Instead of randomly selecting 10% of the nurses in every hospital in the country, you could randomly select 10% of the hospitals and take all of the nurses in those hospitals to be part of your sample.