On the other side of the ledger, higher tuition over time was related to sharply higher financial benefits from a college education. The typical college graduate earned per hour about 50 per cent more than the typical high school graduate in 1980, and the gap is now about 95 per cent. Earnings of graduates with a professional degree or other post-graduate education grew even faster over time than did earnings of college graduates.His main conclusion is that interest rates on student loans should be determined by the amount of income you make after graduating from college:
Within any category of graduates, earnings vary considerably by type of job-- teachers and clergymen earn a lot less than investment bankers--and by degree of success within jobs. Fixed interest loans are not the best way to borrow when loans are used for risky activities. Returns on higher education are rather risky, even after adjusting for how they co-vary with returns on assets. Businesses often borrow with the equivalent of equity to finance start-ups and other risky activities, where the equity pays off well if the venture is successful, and pays little if the venture fails.
This suggests that student loans should not have fixed interest rates that require a fixed amount to be repaid per $1.000 borrowed, but rather should have the equivalent of an "equity" repayment system. That would mean that persons who earn very little repay little, while those who earn a lot repay a lot (per $1,000 borrowed). Requiring individuals who are repaying student loans to submit their income tax statements each year, so that lenders could document what the borrowers earned, could enforce such an income-contingent repayment system.
(Source: Becker-Posner Blog)