The White Cover Snowmobile Association promotes snowmobiling in both the Upper Midwest and the Rocky Mountain region. The industry has been affected in the West because of uncertainty associated with conflicting court rulings about the number of snowmobiles allowed in national parks. The Association advertises in outdoor- and tourist-related publications and then sends out pamphlets, maps, and other regional related information to people who call a toll-free number and request the information. The association orders the packets 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 that will be received in 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
The data are in the file called Winter Adventures.
a. Construct a multiple regression model using all three independent variables. Write a short report discussing the model.
b. Based on the appropriate residual plots, what can you conclude about the constant variance assumption? Discuss.
c. Based on the appropriate residual analysis, does it appear that the residuals are independent? Discuss.
d. Use an appropriate analysis of the residuals to determine whether the regression model meets the assumption of normally distributed error terms. Discuss.