Refer to the data introduced in problem 14.13 on page 565 concerning average weekly earnings of female employees in Australia.

a. Fit a third-order autoregressive model to the earnings data and test for the significance of the third-order autoregressive parameter. (Use α 5 0.05.)

b. If necessary, fit a second-order autoregressive model to the earnings data and test for the significance of the second-order autoregressive parameter. (Use α 5 0.05.)

c. If necessary, fit a first-order autoregressive model to the earnings data and test for the significance of the first-order autoregressive parameter. (Use α 5 0.05.)