My data is clearly non-stationary (by both graphical and formal tests). So I ran code to difference it. When you do that you should retest the differenced data to see if the results need to be differenced again. I am not sure, I can't find in the documentation, how you do that. I assume you test the residuals.
This is the code I ran to difference. I left out the code requesting the formal tests to show it was non-stationary here.
ods graphics on;
proc arima data= tsdata;
identify var=spend(1) ;
run;
ods graphics off;
I am also confused how you do a second difference if the first difference does not work (and ignoring seasonality differencing). I believe it is identify var=spend(1,1) ;
This is the code I ran to difference. I left out the code requesting the formal tests to show it was non-stationary here.
ods graphics on;
proc arima data= tsdata;
identify var=spend(1) ;
run;
ods graphics off;
I am also confused how you do a second difference if the first difference does not work (and ignoring seasonality differencing). I believe it is identify var=spend(1,1) ;