Consider the bearing wear data in Exercise 12-19.

(a) For the model with no interaction, test for significance of regression using   0.05. What is the P-value for this test? What are your conclusions?

(b) For the model with no interaction, compute the t-statistics for each regression coefficient. Using   0.05, what conclusions can you draw?

(c) For the model with no interaction, use the extra sum of squares method to investigate the usefulness of adding x2  load to a model that already contains x1  oil viscosity. Use   0.05.

(d) Refit the model with an interaction term. Test for significance of regression using   0.05.

(e) Use the extra sum of squares method to determine whether the interaction term contributes significantly to the model.

Use   0.05.

(f) Estimate 2 for the interaction model. Compare this to the estimate of 2 from the model in part (a).