No, it's relatively easy to estimate the "net value" of a mortgaged house, which should (except in a housing market crash) be positive, otherwise the bank would

No, it's relatively easy to estimate the "net value" of a mortgaged house, which should (except in a housing market crash) be positive, otherwise the bank wouldn't lend you the money in the first place. On the other hand, it's very very hard to calculate e.g. net "student loan value" (i.e. future earnings - future loan payments) - in fact, many people took out huge student loans but found themselves making way less income than they expected (hoped for)! Unfortunately, lenders don't care about that, becaue the government guarantees the loan...