Monthly gas prices, part 3.

Using the data from Exercise 42, develop and compare the following models.

a) Fit an appropriate autoregressive model by testing for the significance of each autoregressive term.

b) Obtain a forecast for the same week you did in Exercise 42 (May 28, 2007).

c) Compare your forecast to the actual value (by computing APE) and to the forecasts obtained in Exercise 42.

d) Recommend an appropriate model for forecasting this time series.