Quantile dispersion graphs for evaluating and comparing designs for logistic regression models

Designs for 0tting a generalized linear model depend on the unknown parameters of the model. The use of any design optimality criterion would therefore require some prior knowledge of the parameters. In this article, a graphical technique is proposed for comparing and evaluating designs for a logistic regression model. Quantiles of the scaled mean-squared error of prediction are obtained on concentric surfaces inside a region of interest, R. For a given design, these quantiles depend on the model’s parameters. Plots of the maxima and minima of the quantiles, over a subset of the parameter space, produce the so-called quantile dispersion graphs (QDGs). The plots provide a comprehensive assessment of the overall prediction capability of the design within the region R. They also depict the dependence of the design on the model’s parameters. The QDGs can therefore be conveniently used to compare several candidate designs. Two examples are presented to illustrate the proposed methodology. c © 2003 Elsevier Science B.V. All rights reserved.