Choose between different ARIMA models?

[LNA2021]

data ARIMA_ASTHMA_AB;
Set ASTHMA_ab;
step= (Quarter>='2020-Q1');
ramp= time_after;
if Quarter < '2020-Q1' then ramp=0;
Run;
Trial (1);
proc arima data=ARIMA_ASTHMA_AB;
identify var= Preval_qtr_ResprtyAnti (2,4) crosscorr=(step(2,4) ramp(2,4));
estimate p=2 q=(4) input=(step ramp) method=ml outmodel=AB_AS3;
run; quit;
Trial(2);
proc arima data=ARIMA_ASTHMA_AB;
identify var= Preval_qtr_ResprtyAnti (2,4) crosscorr=(step ramp);
estimate p=1 q=(4) input=(step ramp) method=ml outmodel=AB_AS5;
run; quit;

Hello,

I am using ITS (ARIMA) to study the impact of intervention on drug utilzation.

Based on the above codes: My question is when to use crosscorr= [Step(1,4) Ramp(1,4)] and when to use only crosscorr= [Step Ramp]?

I know in order to choose between different ARIMA models, I need to check SBC and AIC (the lower the better model).

Also, I attached the output for both trial 1 and 3 SAS codes. Could you please advise which model is better and why?

Thanks in advance.

[sbxkoenk]

Hello @LNA2021 ,

I have moved your question to the

SAS Forecasting and Econometrics board (under the Analytics header).

You will get much better answers here.

Note there's a lot of literature on this subject.
And many approaches are taken : ARIMA(X) , State Space Models (SSM), Mixed models , ...

But to re-assure you : PROC ARIMA can definitely be used for interrupted time series analysis.

Cheers,

Koen