title: Power and sample size requirements for two-part models.
abstract: Two-part models assume the data has a probability mass at zero and a continuous response for values greater than 0. We construct tests based on the proportion of zeros and the difference among the positive values of a response giving rise to a two degree of freedom chi(2) test. This note gives the non-centrality parameter and finds the power for the test. The power is compared to the simulation results in a recent paper. We derive sample size calculations. We note that some modifications of this procedure may provide better tests if the non-zero responses are discrete. Published in 2001 by John Wiley & Sons, Ltd.
authors: FDA/CBER/Office of Biostatistics and Epidemiology, Food and Drug Administration, Rockville, MD 20852, USA. lachenbruch@a1.cber.fda.gov
authors: P A
authors: PA
authors: Lachenbruch
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D008432:Mathematical Computing; D015233:Models, Statistical; D010043:Outcome and Process Assessment, Health Care / Q000706:statistics & numerical data*; D012984:Software