Andre' Khuri, University of Florida

The Hazards of Coding in Linear Models

Nonsingular linear transformations, such as coding, of the control variables in a linear model are frequently used in regression and response surface models. The common belief is that coding transformations do not change the prediction capability of the model. This is not always true. Predictions can be altered if the model is not well formulated, which may occur if the model is reduced by a variable selection technique. A measure will be introduced to quantify the departure of the model from being well formulated. This measure can also be used to provide some diagnostics that pertain to the change in the model's prediction capability as a result of coding. (Note: This seminar should be of interest to students in regression and linear models courses.)