title: Sample size formulae for intervention studies with the cluster as unit of randomization.
abstract: This paper presents sample size formulae for both continuous and dichotomous endpoints obtained from intervention studies that use the cluster as the unit of randomization. The formulae provide the required number of clusters or the required number of individuals per cluster when the other number is given. The proposed formulae derive from Student's t-test with use of cluster summary measures and a variance that consists of within and between cluster components. Power contours are provided to help in the design of intervention studies that use cluster randomization. Sample size formulae for designs with and without stratification of clusters appear separately.
authors.affiliation: Department of Epidemiology and Social Medicine, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: F Y
authors.initials: FY
authors.lastname: Hsieh
mesh_terms: D002318:Cardiovascular Diseases / Q000209:etiology / Q000401:mortality; D006801:Humans; D009784:Occupational Diseases / Q000209:etiology; D011897:Random Allocation; D012107:Research Design; D012307:Risk Factors; D012494:Sampling Studies; D013223:Statistics as Topic; D014481:United States