Let’s assume we have an ARDL model with 6 variables, to ensure the robustness of the long term relationship, what other technique I can use in the following scenarios: – Data at stationary at level – Data at stationary at level except for one variable which is stationary at first difference. – mixed of data. – Non-stationary data.
I was told to use the cointegration technique to check the robustness of the long term relationship results in the ARDL model. When is cointegration technique applicable in the cases above?