I’ve been tasked by my company to forecast the amount of phone calls on an hourly basis during the company’s opening hours.

That all went pretty well - until I realized, that my company’s opening hours for phone calls is 9am to 3pm (6 hours total) on Mondays and 9am to 12am (3 hours) the remaining weekdays. That implies that I’ve some sort of “unbalanced” timeseries, because of the three extra hours every Monday.

As I see it that completely destroys my chance of utilizing an ARIMA-model, since the AR and MA terms can’t handle the unbalances.

I’ve been searching for some time now, and I really need some sort of strategy for this problem. My currently “fallback” strategy is to use a normal regression with dummies for every hour. This is however maybe not the best way forward.

So what I’m asking is; maybe you guys have experience with a problem like this, that you would like to share, or maybe some literature on the problem.

I’m currently working in SAS with the timeseries module (SAS ETS), so if you know of any procedure, that would also be much appreciated.

Andreas