Hello I was going through this article by Ken Garrett and could not comprehend a particular calculation and I hope you could put this into perspective. Time series analysis Forecasting page 14 of attachment.
Projecting a trend
The article states that there are 5 seasons to the predicted trend and I just cannot understand the calculation.
1120.9 + (7 x 1.7) = 1132.8
Why should the calculation not be
1120.9 + (5 x 10.8) = 1174.9
In my understanding, the trend has increased from 1002.10 to 1120.9 in 11 periods hence the figure 10.8 for the incremental increase and we have 5 seasons to project hence 5.