Consider the semiconductor HFE data in Exercise 12-9.

(a) Plot the residuals from this model versus . Comment on the information in this plot.

(b) What is the value of R2 for this model?

(c) Refit the model using log HFE as the response variable.

(d) Plot the residuals versus predicted log HFE for the model in part (c). Does this give any information about which model is preferable?

(e) Plot the residuals from the model in part

(d) versus the regressor x3. Comment on this plot.

(f) Refit the model to log HFE using x1, x2, and 1x3, as the regressors. Comment on the effect of this change in the model.