Things That Make You Go Hmm, Brookings Edition

Brookings questions the value of ban the box legislation and includes this gem:

[E]mployers might prefer applicants with a college degree not because of what one learns in college but because earning that degree is correlated with greater motivation, intelligence, and diligence – unobservable characteristics that make you a more productive employee.

If the characteristics are unobservable, how do we know they correlate with earning a degree or being a more productive employee?

Image by xkcd, but you already knew that.