A Brief Introduction

Abstract

This book deals with a class of models that pertain to data consisting of the values of p + 1 variables y, x ₁, x ₂, …, x _p taken on each of n “observational units.” We refer to y as the response variable (regardless of whether it actually makes sense to think of y as a response to anything) and to x ₁, …, x _p as the explanatory variables (regardless of whether they actually help to explain anything). Let y _i, x _i1, x _i2, …, x _ip represent the observed values of these variables for the ith observational unit.