Diagnostics and Transformations for Simple Linear Regression

In Section 3.1, we start by examining the important issue of deciding whether the model under consideration is indeed valid. In Section 3.2 , we will see that when we use a regression model we implicitly make a series of assumptions. We then consider a series of tools known as regression diagnostics to check each assumption. Having used these tools to diagnose potential problems with the assumptions, we look at how to first identify and then overcome or deal with a common problem, namely, nonconstant error variance.