Rapid advances in technology have had a profound impact on the United States recording industry (The New York Times, July 28,2008). While cassette tapes gave vinyl records strong competition, they were subsequently eclipsed by the introduction of the compact disc (CD) in the early 1980s. Lately, the CD, too, has been in rapid decline, primarily because of Internet music stores. The following data show a portion of year-end shipment statistics on the three formats of the United States recording industry, in particular, the manufacturers unit shipments, in millions, of vinyl, cassettes, and CDs from 1991 to 2008. The full data set can be found on the text website, labeled Recording Industry.
a. Plot the series for cassettes. Estimate the quadratic and the cubic trend models for this series. Make a forecast with the chosen model for 2009.
b. Plot the series for CDs. Estimate the linear and the quadratic trend models for this series. Make a forecast with the chosen model for 2009.