I'm using the TBATS model of the forecast package with Google Analytics data, to forecast web trafic containing multiseasonal effects (msts).

I have two year of daily data that contains two columns like these :

date           sessions
2015-01-01     2667
2015-01-02     3542
2015-01-03     2383
2015-01-04     2772
2015-01-05     7797
2015-01-06     7599

I made one forecast for all my data and another forecast with data containing only a segment of users.

In the first case (all data), I obtained this result :

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And in the second case (segment data), I obtained this :

enter image description here

My questions :

  1. How to interpret the slope component? I get it in the first case but not in the second. Is there a reason for that?
  2. What could do that the Lo/Hi points are so much wider in the second case?

1 Answer 1


In your first example two years of annual data was used with no apparent effects due to omitted variables like price , promotion etc or level shifts . The two years of forecasts are visually identical with presumptive symmetric forecasting confidence limits totally ignoring any unusual activity in the future. Your second example based upon only 1 year of data has less predictability (fitting statistics ... smaller r-square ...larger error variance) thus wider limits would be expected as no seasonal component was identifiable due to only 1 year of data.

  • $\begingroup$ if you post your data I will take a look at it and provide you with a model that will convert your data to information and perhaps some knowledge/insight.. Please specify the starting date and the country of origin. $\endgroup$
    – IrishStat
    Apr 9, 2017 at 1:27

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