That's what banks do to manage their credit risk, they look at defaults rates "through the cycle", i.e. including the last downturn. But for new asset classes, like subprime in their time and like student loans now (if you look at chart in the article in term of growth), people have to make their own assumptions in term of how it will behave in a downturn. And that's where the credit markets can be really dangerous. These assumptions are what banks and rating agencies got wrong last time. And I think it is fair to assume that people under financial hardship will probably default on their student loan before they default on their mortgage (roof over their head) or their car.
