F IL E Rock'n'roll is a form of music that evolved in the United States and very quickly spread to the rest of the world. The interest in rock music, like any other genre, has gone through ups and downs over the years. The Recording Industry Association of America (RIAA) reports consumer trends on the basis of annual data on genre, form at, age, and gender of purchasers and place of purchase. The accompanying table lists a portion of the percentage (share) of total shipm ent o f music that falls in the category of rock music from 1990–2008. The full data set can be found on the text website, labeled Rock Music.

Y e a r S h a r e 1991 34.8 1992 31.6

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2008 31.8 Source: w w w .riaa .co m .

a. Plot the above series and discuss the presence of random variations.

b. Use a 3-period moving average to make a forecast for the share of rock music in 2009.

c. Use a 5-period moving average to make a forecast for the share of rock music in 2009.

d. Use the MSE to pick the appropriate moving average for making a forecast for the share of rock'n'roll music in 2009.