1. Julie has collected data on other variables that were not included in her multiple regression model. Should one or more of these other variables be included in her model? More generally, how can Julie be sure she has the "right" set of predictor variables?
2. Assuming there are no additional important predictor variables, are you satisfied with Julie's forecasting model? How would you "sell" the model to management (and Jackson Tilson)?
3. How might Julie's model be used to determine future amounts spent on newspaper and TV advertising?
4. What conditions might prompt Julie to reexamine her regression model or, perhaps, to look for another method of forecasting sales?
In Example 1.1, Julie Ruth collected monthly sales data on her company along with several other variables she thought might be related to sales. Her forecasting efforts using these data along with Minitab are detailed in Cases 2-3, 3-4, and 5-6. Her desire to improve the accuracy of her forecasts suggested the use of multiple regression.