title: Statistical power in three-arm cluster randomized trials.
abstract: This article shows how to compute statistical power for testing the main effect of treatment in three-arm cluster randomized trials. Using orthogonal coding, we derive the exact test statistic of the treatment effect and its non-central distribution. The non-centrality parameter in the omnibus test is found to be related to the non-centrality parameters in the contrast tests. A study of physician and pharmacist comanagement of patients' blood pressure is used as an example to show the power computation in a three-arm cluster randomized trial.
authors.affiliation: Department of Educational Studies, University of South Carolina, Columbia, SC, USA xliu@mailbox.sc.edu.
authors.forename: Xiaofeng Steven
authors.initials: XS
authors.lastname: Liu
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D015233:Models, Statistical; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012107:Research Design; D013223:Statistics as Topic
keywords: cluster randomized trial; sample size; statistical power