To establish that your previously cited factoid had any significance.
Are you willing to make that up-front admission?
What "admission"? You have on the table a factoid that on its own proves nothing; you can leave it at that if you like, or you can attempt to establish its significance by getting some related numbers.
That you're willing to admit up front that if the Alaskan teen numbers today are about equal to the rest of the nation, it means that legalization for Alaskan adults did impact teen use.
I got the link from TKDietz. I'll post it upon seeing your admission.
As I said before, without your admission, why bother doing the work?