Chapter 17.6, Problem 37E

The quarterly sales data (number of copies sold) for a college textbook over the past three years follow.

1. a. Construct a time series plot. What type of pattern exists in the data?
2. b. Show the four-quarter and centered moving average values for this time series.
3. c. Compute the seasonal and adjusted seasonal indexes for the four quarters.
4. d. When does the publisher have the largest seasonal index? Does this result appear reasonable? Explain.
5. e. Deseasonalize the time series.
6. f. Compute the linear trend equation for the deseasonalized data and forecast sales using the linear trend equation.
7. g. Adjust the linear trend forecasts using the adjusted seasonal indexes computed in part (c).