文档介绍：Dr. Allan Donner Dr. Neil Klar Learning Objectives ? To distinguish experimental trials based on the unit of randomization (. individual, family, community). ? To appreciate the consequences of cluster randomization on sample size estimation and data analysis. ? To identify key features of a cluster randomization trial which need to be included in reports. What Are Cluster Randomization Trials? Cluster randomization trials are experiments in which clusters of individuals rather than independent individuals are randomly allocated to intervention groups. Example 1: Study Purpose : To evaluate the effectiveness of Vitamin A supplements on childhood mortality. ? 450 villages in Indonesia were randomly assigned to either participate in a Vitamin A supplementation scheme, or serve as a control. ? One year mortality rates pared in the two groups. Sommer et al. (Lancet, 1986) Example 2: Study Purpose : To promote smoking cessation munity resources . ? 11 munities were selected and one member of each pair was randomly assigned to the intervention group. ? 5-year smoking cessation rates pared in the two groups. ? Communities were matched on demographic characteristics (. size, population density) and geographical proximity. COMMIT Research Group (Am J Public Health, 1995) Example 3: Study Purpose : To evaluate the effectiveness of treated nasal tissues versus standard tissues. ? 90 families were selected and randomized to one of the two intervention groups separately in each of three family size strata (2, 3, or 4 members per family). ? 24-week incidence of respiratory illness were compared in the two groups. Farr et al. (Am. J. Epid., 1988) Reasons for Adopting Cluster Randomization ? Administrative convenience ? To obtain cooperation of investigators ? Ethical considerations ? To enhance pliance ? To avoid treatment group con