TWO STAGE CLUSTER RANDOM SAMPLING – Samples chosen from pre-existing groups. Groups are selected and then the individuals in those groups are used for the study.
If we wished to know the attitude of fifth graders in Connecticut about reading, it might be difficult and costly to visit each fifth grade in the state to collect our data. We could randomly select 10 schools (our clusters) and survey the students in those schools. Each school in the state would have an equal chance of being selected, but only the students at the selected schools would be surveyed.
An extension of the Cluster Random Sample is the TWO-STAGE RANDOM SAMPLE. In this situation, the clusters (classes in our example) are randomly selected and then students within those clusters are randomly selected.