Graphical Aids for Nonlinear Regression and Discriminant Analysis

Abstract

In nonlinear regression and discriminant analysis applications, graphical displays can facilitate understanding and communication with subject area researchers. For nonlinear regression, Cook-Weisberg confidence curves, Wald intervals, and contour plots of the loss function in the parameter space provide information about the certainty of estimates and also about estimates of functions of parameters. For linear and quadratic discriminant analysis models, scatterplots bordered by box plots aid transformation selection as the data analyst uses a GUI to quickly transform plot scales. A lasso plot tool provides a link from points (cases) in displays to a data worksheet with all values. Within-group histograms help outlier detection and to study the spread across groups. A failure of the equal covariance matrix assumption may be seen in within-group scatterplot matrices embellished with ellipses of concentration. Enhancements to canonical variable plots allow easy identification of misclassified cases.