<p>^None that I know of. The differential is generally due to the fact that law, business, and medical school faculty have many opportunities for lucrative careers outside academia, which is not the case for most arts and sciences faculty (with the exception of those in economics and, to a lesser extent, some of the sciences). The other reason for the differential has to do with grant and other outside funding opportunities, which are available much more readily to those in medical and scientific fields than to those in the social sciences and, especially, to those in humanities.</p>