title: A planning tool for two-phase case-control studies.
abstract: We present a software tool for planning two-phase case-control studies assuming categorical covariates. Two-phase designs, in which validation or complete information data are sampled stratified both on a dichotomous outcome and a covariate from a first-phase study with incomplete data, result in efficient estimates compared to standard designs. Efficiency and power depend on sample size, sampling fractions within each stratum x outcome cell, distributional assumptions and the regression model. Our software, called Two-Phase Planning Tool (or 2P Planning Tool), offers a graphical user interface (GUI) to organize and input the relevant anticipated entities and calculates a normed, expected two-phase case-control study. The 2P Planning Tool is especially helpful in selecting a stratification. The data are output into an Excel-sheet, which in turn can be read into a standard statistics package to perform "experimental" power calculations. Its use is illustrated by an example from epidemiology. Software for analyzing logistic two-phase studies is also provided.
authors.affiliation: Bremer Institut für Präventionsforschung und Sozialmedizin, Linzer Str. 10, D-28359 Bremen, Germany. schill@bips.uni-bremen.de
authors.forename: Walter
authors.initials: W
authors.lastname: Schill
authors.forename: Pascal
authors.initials: P
authors.lastname: Wild
authors.forename: Iris
authors.initials: I
authors.lastname: Pigeot
mesh_terms: D016021:Epidemiologic Studies; D005602:France; D006801:Humans; D015233:Models, Statistical; D010934:Planning Techniques; D012984:Software; D014584:User-Computer Interface