Chapter 16, Problem 27PS

Using the data for Problem 16.15 on page 646 that represent U.S. total computer and software sales $\left(\text{in Smillions}\right)$ from 1992 through 2012 (stored in ComputerSales),

a. fit a third-order autoregressive model to the total sales and test for the significance of the third-order autoregressive parameter. $\text{(Use }\alpha =\mathrm{0.05.})$

b. if necessary, fit a second-order autoregressive model to the total sales and test for the significance of the second-order autoregressive parameter. $\text{(Use }\alpha =\mathrm{0.05.})$

c. if necessary. fit a first-order autoregressive model to the total sales and test for the significance of the first-order autoregressive parameter. $\text{(Use }\alpha =\mathrm{0.05.})$

d. if appropriate, forecast the total sales in 2013.