Mary Katharine Ham wonders if Krugman's Ph.D. is in Epistemic Closure, not economics. After reading this squib from Krugman, it's a legitimate question:
Some have asked if there aren’t conservative sites I read regularly. Well, no. I will read anything I’ve been informed about that’s either interesting or revealing; but I don’t know of any economics or politics sites on that side that regularly provide analysis or information I need to take seriously. I know we’re supposed to pretend that both sides always have a point; but the truth is that most of the time they don’t. The parties are not equally irresponsible; Rachel Maddow isn’t Glenn Beck; and a conservative blog, almost by definition, is a blog written by someone who chooses not to notice that asymmetry. And life is short …
Bear in mind that this paragraph comes right after Krugman lists a lot of perfectly respectable (though shamelessly ideological and hyperbolic) liberal blogs.
So in other words, if you're reading this you're probably more informed than at least one Nobel Prize Winner.