Hello -
This example might get you started: http://support.sas.com/rnd/app/examples/ets/tourism/index.htm
Having said this please allow me to propose an alternative for you to consider. First I'd like to point you to some research on usefulness of complexity in forecasting models, which is worth reading: http://www.kestencgreen.com/simplefor.pdf
I'm assuming that your goal is to forecast sales - and take gas price and events into account as dependent variables.
If that is the case than the following approach might work:
Build an ARIMAX or UCM model which uses gas price and event as inputs and sales as output. These models will be able to incorporate cross-correlation effects (between price and sales for example) in a dynamic fashion. Some people refer to these models as dynamic regression. The more tricky part is too figure out if price and sales are cross-correlated indeed.
Of course you will also need to forecast the gas price - either by a statistical model such as exponential smoothing or by assuming future values yourself.
After successfully building your model - and assuming price was significant - you can run some what-if scenarios (change the future values of price) to see how your model is behaving.
There are several ways to do such analysis in SAS - SAS Visual Analytics provides this functionality to some extend. SAS Forecast Server (or SAS Forecasting for Desktop) would be my tool of choice - but I'm biased. SAS/ETS provides you to a couple of procedures which will allow you to implement the approach above yourself - check out the following procedures: TIMESERIES, ARIMA, UCM, and ESM.
Of course if you don't agree with my statements above you can also revert back to VARMAX and start with the example I shared earlier.
Happy Friday,
Udo
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