Use the output from Problem 11 in Chapter 8 and the output given here to answer the following questions. (Assume that no interaction occurs between TV advertising expenditure [X1] and print advertising expenditure [X2].)
a. Does the print advertising expenditure confound the relationship between sales (Y) and TV advertising expenditure (X1)?
b. Should print advertising expenditure be included in a model that already contains TV advertising expenditure, based on considerations of precision?
c. In light of your answers to parts (a) and (b), should the final model include both types of advertising expenditures as predictors? Explain.