The quarterly sales levels (measured in millions of dollars) for Goodyear Tires are shown in the Table.

 

1. Does there appear to be a significant seasonal effect in these sales levels? Plot the time series.
2. Perform the decomposition analysis using multiplicative & additive models.
3. Analyze this time series to get the four seasonal Indexes and interpret the indexes and determine the extent of the seasonal component in Goodyear's sales?
4. Forecast sales for the four quarters of 2007 for each model and compare the result & comment on them.

Show all Minitab Output                                                                

 

Year Quarters Y, 2000 1 2 500 350 3 250 4 400 2001 450 350 6 7 200 8 300 350 200 150 2002 10 11 12 13 14 15 16 400 2003 550 350 250 550 2004 17 18 550 400 19 350 20 600 2005 21 22 750 500 400 23 24 25 26 650 2006 850 600 27 450 28 700