time series

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August 9, 2014 at 4:02 pm #188951
fauz
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The following variations and trend have been calculated for sales over a period of time using additive model:

seasonal variation
quarter 1 +25
quarter 2 -10
quarter 3 -30
quarter 4 +15

trend +50 per quarter
the last known trend reading was taken in year 3,quarter 3 and was $1750

Question:what would be the time series value for year 4 quarter 3?

please help!!!!
August 9, 2014 at 4:16 pm #188960
John Moffat
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The last trend reading was year 3 quarter 4. So, by year 4 quarter 3, three more quarters have passed. So the trend forecast will be 1750 + (3 x 50) = 1900.

Quarter 3 has a seasonal variation of -30, so the actual forecast for year 4, quarter 3 will be 1900 – 30 = 1870.
August 9, 2014 at 4:22 pm #188965
fauz
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thanks for the reply sir, but the answer on the answer sheet is $1920. I’m confused.
August 9, 2014 at 4:24 pm #188967
John Moffat
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Sorry – my fault.

There are four more quarters (not three) from year 3 quarter 3 to year 4 quarter 3.

So the trend forecast will be 1750 + (4 x 50) = 1950.

Quarter 3 has a seasonal variation of -30, so the actual forecast is 1950 – 30 = 1920.
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