The following data list worldwide shipments of personal computers (in thousands) according to Dataquest.
Year Shipments (in thousands) 1990 23,738 1991 26,966 1992 32,411 1993 38,851 1994 47,894 1995 60,171 1996 71,065 1997 82,400 1998 97,321
a) Use exponential smoothing to determine the forecast of shipments for the year 1999. Use the actual shipments for 1990 as the starting forecast for 1991. Use a smoothing constant of a = 0.4.
b) Plot the data, fit a trend line, and discuss the strength of prediction of the regression model.
c) Use the regression model to predict the shipments for the year 1999.
d) Compare the two forecasts. Which forecast would you prefer to use and why?