8.7 Consider the quarterly number of international tourists to Australia for the period 1999-2010. (Data set aus tou.ris ts.)

(a) Describe the time plot.

(b) What can you learn from the ACF graph?

(c) What can you learn from the PACF graph?

(d) Produce plots of the seasonally differenced data (1 - B4)Yt. What model do these graphs suggest?

(e) Does auto. a.rima give the same model that you chose? If not, which model do you think is better?

(f) Write the model in terms of the backshift operator, and then without using the backshift operator.