The closing value of the Dow Jones Industrial Average for each trading day during a one-year period is provided in the file P12_19.xlsx.
a. Using a span of 2, forecast the price of this index on the next trading day with the moving average method. How well does the moving average method with span 2 forecast the known observations in this series?
b. Repeat part a with a span of 5; with a span of 15.
c. Which of these three spans appears to be most appropriate? Justify your choice.