If the purpose of the time series modelling is to build one that gives the most accurate forecast, may I ask if it necessary to check the model AIC to determine the optimal lag when you can iteratively check the forecast RMSE at all possible lags and determine the lag that gives the lowest RMSE? Also, is it unusual that the model that gives the lowest RMSE may not necessarily has the minimum AIC?
Time Series Forecasting – Purpose of Model AIC vs. Forecast RMSE at Each Lag
aicforecastingmodel selectionrmstime series
Best Answer
Is it necessary to check the model AIC? No. But it can be a good idea.
*Meanwhile, using RMSE without splitting the dataset is just going to select the most flexible of the candidate models, and that will in all likelihood be overfitting.