Using the average baseball salary from 2000 through 2012 data for Problem 16.18 on page 626 (stored in BBSalaries).
a. Fit a third-order autoregressive model to the average baseball salary and test for the significance of the third-order autoregressive parameter. (Use a =0.05.)
b. If necessary, fit a second-order autoregressive model to the average baseball salary and test for the significance of the second-order autoregressive parameter. (Use a = 0.05.)
c. If necessary, fit a first-order autoregressive model to the average baseball salary and test for the significance of the first-order autoregressive parameter. (Use a = 0.05.)
d. Forecast the average baseball salary for 2013.