Clinical Trials

■■❚❙❘Chapter 15Cluster RandomizedTrialsUmair Mallick, Ameet Bakhai, Duolao Wang,and Marcus FlatherWhile conventional trials randomize individual subjectsto different treatments, cluster randomized trials use agroup of individuals, a hospital, or a community as the unitof randomization. Cluster randomized trials are increasinglyused in primary care, health promotion, and public health,where the methodological superiority of these trials has beenproven when compared with conventional randomized trials.Cluster randomized trials potentially require a much largernumber of individuals in the trial if there is a high likelihoodfor similar outcomes between individuals, since otherwise thepower of such trials to detect a significant difference is muchlower than conventional randomized trials. In this chapter,we provide an overview of cluster randomized trials alongwith their design, analysis, and ethical implications.141