(For bachelors degrees): Each year, they will calculate the median earnings 4 years after graduation of graduates of every (Institution, CIP code) tuple. (CIP Code: 6 digit code that identifies a "program"; there are ~2,000).
Then they calculate the median earnings of high school grads in that Institution's state across all jobs.
If the high school grads earn more than the bachelors degree grads for 2 out of the past 3 years, the Feds won't offer student loans for that (Institution, CIP code) tuple.
Incidentally, the IRS already supplies this data in aggregated form to the US Dept. of Ed.
Check it out here: https://collegescorecard.ed.gov/
Here is MIT: https://collegescorecard.ed.gov/school/?166683-Massachusetts...