Times series analysis — OpenTuition Forums

Zzwahira12y ago

dear sir can you help me with these two questions? 1.A product has a constant(flat)trend in its sales, and is subject to quarterly seasonal variations as follows: Quarter Q1 Q2 Q3 Q4 Seasonal +50% +50% -50% -50% sales last quarter, Q2 were 240 units Assuming a multiplicative model for the time series, predicted unit sales for the next quarter will be closet to A.80 B120 C160 D320 2.In a time series analysis, using additive model, at a certain time, the following data is obtained. Actual value 170 Trend 182 Seasonal Value -12.8 The residual value at this point is A-0.8 B0.8 C-24.8 D24.8

John MoffatTutor12y ago#1

1) If the trend is constant, it would mean that if there were no seasonal variation then we would expect sales in the next quarter (Q3) to be 240. However, there is a seasonal variation in Q3 of -50%, so the actual forecast for Q3 will be 240 - (50% x 240) = 120. 2) Our forecast would the trend (182) adjusted by the seasonal variation ( -12.8) which would be 182-12.8 = 169.2 The actual figure is 170. So the difference is 170 - 169.2 = +0.8

Zzwahira12y ago#2

Thanks you sir

John MoffatTutor12y ago#3

You are welcome :-)

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