Exercise 12-10 presents data on heat treating gears.
(a) Test the regression model for significance of regression. Using a = 0.05, find the P-value for the test and draw conclusions.
(b) Evaluate the contribution of each regressor to the model using the t-test with a = 0.05.
(c) Fit a new model to the response PITCH using new regressors x1 = SOAKTIME SOAKPCT and x2 = DIFFTIME DIFFPCT.
(d) Test the model in part (c) for significance of regression using a = 0.05. Also calculate the t-test for each regressor and draw conclusions.
(e) Estimate σ2 for the model from part (c) and compare this to the estimate of 2 for the model in part (a). Which estimate is smaller? Does this offer any insight regarding which model might be preferable?