Greg Mankiw links to GRE test results (the test done before graduate school) that show scores by discipline. Physics ranks first with economics number 4. Public administration is a bit of a worry.
That reminded me of an old story (not sure if it is true) about a discussion between economics Nobel prize winner, Bob Solow, and a physics prize winner. Solow was report to have commented that he always thought physicists were smarter than economists. The physicist was said to have replied “well I don’t think that can be true. Otherwise people would move from physics to economics until their average intelligence was equal.”