I have two models. One applies a seasonal difference, one applies a seasonal and non seasonal difference. The latter is stationary according to the ADF test, the former is not. But the former passes the Box Ljung test, meaning there is no serial correlation, and later one (the one that is stationary) does not - its not close. Also the one that is stationary generates numbers that are completely impossible for our organization (they are totally impossible given past spending, absurdly so).
I have been unable to find any model that is stationary according to the ADF that generates realistic numbers or passes the Box Ljung test for no serial correlation.
I have been unable to find any model that is stationary according to the ADF that generates realistic numbers or passes the Box Ljung test for no serial correlation.