A popular brand of tennis shoe has had the following demand history by quarters over a three-year period.

1990 Demand 1991 Demand 1992 Demand
1 12 1 16 1 14
2 25 2 32 2 45
3 76 3 71 3 84
4 52 4 62 4 47

a. Determine the seasonal factors for each quarter by the method of centered moving averages.
b. Based on the result of part (a), determine the deseasonalized demand series.
c. Predict the demand for the first quarter of 1993 for the deseasonalized series from a six-quarter moving average.
d. Using the results from parts (a) and (c), predict the demand for the shoes for the first quarter of 1993.
e. Compare the result from part (a) with seasonal factors obtained by the simpler method described at the beginning.