Appendix I. Commonly Used Parameterizations in Logistic Regression Models

  • I.1 Introduction 509

  • I.2 The 'Reference' Parameterization 509

  • I.3 The 'Effect' Parameterization 511

  • I.4 More Than Two Nominal Levels 512

  • I.5 Other Parameterizations 515

I.1 Introduction

There are several ways in which a statistical model may be written. In a logistic regression model (Chapter 20), you might include numeric covariates (either continuous or ordinal) and nominal categorical factors. Generally, you will have one parameter (βi) associated with each numeric covariate (Xi). For a nominal covariate (or any effect used in a CLASS statement in SAS), the number of parameters depends on your model specification or 'parameterization' as well as the number of levels of the ...

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