Our professor keeps on writing in his slides that when you test different ARIMA models on your time series, one always has to keep T fixed.
I assume he is talking about fitting your model using the same number of observations. If you try a model with a higher lag, you loose one observation to fit the data on. Is this correct?
Is this why he writes restrict your sample? We have 214 observations, should I for example to be on the safe side only use 205 observations? And how does Eviews know to always use the same number of obersations?
Thanks in advance.