cluster randomized trial, cluster randomized controlled trial, group randomized trial
In cluster randomized studies, commonly called cluster randomized trials, groups - for example, primary care practices, or schools, and the individuals within them - rather than individuals are randomly allocated to one of two or more treatments (e.g. different health education programmes).
One reason for doing this is to avoid the inadvertent application of the treatment allocated to one of the treatment comparison groups to people in the other treatment comparison group (contamination).
Another reason is to assess treatments administered to a group rather than to individuals. When clusters of people are allocated rather than individuals, care should be taken to avoid unit of analysis errors.
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