title: Comparison of a two-stage and three-stage interim-analysis procedure.
abstract: A statistical model for combining p values from multiple tests of significance is used to define rejection and acceptance regions for two-stage and three-stage sampling plans. Type I error rates, power, frequencies of early termination decisions, and expected sample sizes are compared. Both the two-stage and three-stage procedures provide appropriate protection against Type I errors. The two-stage sampling plan with its single interim analysis entails minimal loss in power and provides substantial reduction in expected sample size as compared with a conventional single end-of-study test of significance for which power is in the adequate range. The three-stage sampling plan with its two interim analyses introduces somewhat greater reduction in power, but it compensates with greater reduction in expected sample size. Either interim-analysis strategy is more efficient than a single end-of-study analysis in terms of power per unit of sample size.
authors.affiliation: Department of Psychiatry and Behavioral Sciences, University of Texas Medical School.
authors.forename: J E
authors.initials: JE
authors.lastname: Overall
authors.forename: R S
authors.initials: RS
authors.lastname: Atlas
mesh_terms: D015982:Bias; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data*; D003627:Data Interpretation, Statistical; D006801:Humans; D015233:Models, Statistical; D011619:Psychotropic Drugs / Q000627:therapeutic use
chemical_list: D011619:Psychotropic Drugs