I am currently dealing with some monthly data on interest rates which goes back over thirty years.
The total 30 years worth of data is I(1). However when I shorten this data to go back only 10 years its I(2).
When running this data in a VECM for the 10 year interval, do I have to difference or log the variable it for it to be I(1) or is it more appropriate just to treat it like an I(1) variable (since the true nature of the process is I(1)) and put it in the VECM even though the 10 years worth of data is I(2)?