The White Cover Snowmobile Association gives out pamphlets, maps, and other tourist-related information to people who call a toll-free number and request the information. The association orders the packets of information from a document-printing company and likes to have enough available to meet the immediate need without having too many sitting around taking up space. The marketing manager decided to develop a multiple regression model to be used in predicting the number of calls during the coming week. A random sample of 12 weeks is selected, with the following variables:

y = Number of calls x1 = Number of advertisements placed the previous week x2 = Number of calls received the previous week x3 = Number of airline tour bookings into Western cities for the current week These data are in the file called Winter Adventures.

a. Develop the multiple regression model for predicting the number of calls received, using backward elimination stepwise regression.

b. At the final step of the analysis, how many variables are in the model?

c. Discuss why the variables were removed from the model in the order shown by the stepwise regression.