You are given an annual time series with 40 consecutive values and asked to fit a fifth-order autoregressive model.

(a) How many comparisons are lost in the development of the autoregressive model?

(b) How many parameters do you need to estimate? 

(c) Which of the original 40 values do you need for forecasting?

(d) State the fifth-order autoregressive model.

(e) Write an equation to indicate how you would forecast j years into the future.