Hello,   I'm trying to use PROC X12 to measure the effect of different calendar months on used vehicle prices.  Basically, I just want a coefficient that I can apply to a baseline price forecast (which is generated by OLS regression), that will adjust the baseline forecast up or down depending on what month it is.  For instance - "All things equal, used vehicle prices are 20% higher in March, so therefore if X(March) = 1, then B(March) = 1.2 and the baseline forecast would be increased by 20%".   Can this be done with Proc X12?  I know as an alternative I could create dummy variables for each calendar month and add those to the OLS regression to capture the same effect, but I'm wanting to try a different approach.  There are no time-series elements in my data (all observations are unique and uncorrelated - they are vehicles that were sold at auction), so I don't need any of the ARIMA functionality within X12.   Thanks,  ... View more