There’s no need to measure anything. The problem with student loans is qualitative. Banks are allowed to make unsecured loans and the borrowers can’t usefully declare bankruptcy. Colleges have every reason to raise prices and lenders have no skin in the game. It isn’t any more complicated, and no amount of data analysis can possibly refute this.
so change the bankruptcy laws. that doesn't require forgiving the loans.
It should surprise nobody that the banking interests (and industry-adjacent politicians) who pushed so hard for student debtors to be uniquely deprived of their right to shed their debt through the courts are now pushing for taxpayers to repay their unsecured loans.