Hi my question is Trend Y=5000+4000x Where Y= quarterly sales volume in units X= the quarter number ( where the first quater of 2009 = quater 17, the second quarter of 2009= quarter 18 etc) Seasonal variations
Quater seasonal variation(units) 1 +3000 2 +1000 3 -1500 4 -2500 What would be the time series forecast of sales units for the third quater of 2010?
You would first forecast the trend by using the equation given and putting x as being 23 (because the first quarter of 2009 is 17, and the third quarter of 2010 (the following year) is 6 quarters later).
Then you would adjust by the seasonal variation and therefore subtract 1500.