For the situation, data, and variables described in Exercise 17.15, perform conventional multiple regression and stepwise regression analyses on the data, then compare the results of the two approaches. The data are in file XR17015.
In exercise
The personnel director of the communications firm in Exercise 17.5 has just provided another variable describing the company’s technical sales representatives: their scores on a sales aptitude test they were recently given. Using data file XR17015, with y = average dollar sales per call, x1 = years of experience, and x2 = score on the sales aptitude test, fit a second-order model with interaction to the data. Interpret the R2 value for the model and indicate whether, at the 0.05 level, the model is significant.
We suggest that Minitab users specify alpha-to-enter as 0.05 and alphato- remove as 0.10.