The exact variance of the average treatment effect estimator in cluster randomized controlled trials
Summary In cluster randomized controlled trials (CRCTs) with finite populations, the exact design-based variance of the Horvitz–Thompson (HT) estimator of the average treatment effect (ATE) depends on the joint distribution of unobserved, cluster aggregates of potential outcomes and is therefore not point-identified. We study a two-stage sampling design in which clusters are sampled at random, units are then sampled within selected clusters, and treatment is assigned at the…