13.65 You have been asked to develop a model using multiple regression that predicts the retail sale of beef and veal combined using time series data. The data file Beef Veal Consumption contains a number of variables related to the beef and veal retail markets beginning in 1935 and extending through the present.

a. Prepare a model that includes a test and adjustment for serial correlation. Discuss your model and indicate important factors that predict beef sales.

b. Prepare a second analysis, but this time include only data beginning in the year 1980.

c. Compare the two models estimates in a and b.