involve randomized assignment of interventions at the level of natural groupsororganizations rather than at the level of patients or other individuals. That is, sets of clinics, hospitals, nursinghomes, schools, communities, or geographic regions are randomized to receive interventions or comparators.Such designs are used when it is not feasible to randomize individuals or when an interventionis designedtobe delivered at a group or social level. These are also known as “group,” “place,” or “community” randomizedtrials.