Brief: I am running Arima model of store data and trying to predict store growth . Inputs : 2018 - 2021 ( Monthly data) store data and forecasting 2022-2026 using one store variable only.
Model : Arima ( (p,d,q) seasonal=(P,D,Q) m =12) Using grid search for multiple p,d,q and P,D,Q values running the different scenario
Running the model, future forecast values have a constant growth , please can someone guide why year on year growth is remaining constant. It becomes difficult to forecast . Should I add something different to above arima model so that I can get a different growth rate for future values.