Validating a model using residual plots, formal hypothesis tests and descriptive
statistics would be quite frustrating if discovery of a problem meant restarting
the modeling process back at square one. Fortunately, however, there are also
techniques and tools to remedy many of the problems uncovered using residual
analysis. In some cases the model validation methods themselves suggest
appropriate changes to a model at the same time problems are uncovered.
This is especially true of the graphical tools for model validation, though
tests on the parameters in the regression function also
offer insight into model refinement. Treatments for the various model
deficiencies that were diagnosed in Section 4.4.4. are
demonstrated and discussed in the subsections listed below.