Refer to Example 8.5. Using the Sears data in Table 8-5, convert the sales and disposable income values to simple differences. That is, create the numbers Y't = Yt - Yt-1 and X't = Xt - Xt-1. Fit a simple linear regression model to the differenced data. Compare your results to the results obtained by the method of generalized differences in Example 8.5. Did you expect them to be much different? Explain.