= Cluster-randomized trial
A cluster-randomized trial assigns whole groups, such as institutions, to an intervention rather than assigning individuals separately. Positive <intraclass correlation> reduces independent information: the equal-size exchangeable approximation has <design effect> $1+(m-1)\rho$ for cluster size $m$. The number of independent randomized clusters also matters for inference. Cluster assignment does not itself remove requirements for <informed consent> or justify dropping outcome ascertainment in the control arm.
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