The GNP for each quarter of the past four years is shown in the following table:
(a) Find the optimal value of a that would minimize MAPE for the exponential smoothing model.
(b) What is the linear trend equation that best fits the data? Forecast the GNP for the first quarter of year 5 by using this equation.
(c) Forecast the GNP for the first quarter of year 5 by using a four-period moving average.
(d) Which of these methods is most appropriate to use? Justify your answer.