Increasing Income Inequality in Higher Education
In 1985-1986, an assistant professor of business (finance, accounting, marketing) earned 48.5% more on average than an assistant professor of English, according to the American Association of University Professors' 2006-07 Report on the Economic Status of the Profession. In the 2005-2006 academic year, the average assistant professor of business earned more than twice as much as an assistant professor of English nationwide (see chart above, click to enlarge). Like the general public, the AAUP is so concerned with income inequlity that its salary report this year is titled "Financial Inequality in Higher Education," which states that "Financial inequality is growing in U.S. higher education. We observe increasing differences between the endowments of rich and poor institutions, between the salaries of college and university presidents and their faculties, between the salaries of athletic coaches and professors, and between well and poorly compensated faculty members. This economic inequality has the potential to negatively affect higher education."
The AAUP doesn't say exactly how increasing income inequality would "negatively affect higher education," and doesn't say exactly what should be done about it, but at least it does recognize the significant contribution of opportunity cost in explalining salary differentials between disciplines like business and English.
Note also that except for business and economics, and to a lesser extent computer science, and psychology, pay in most disciplines relative to English has been fairly constant, even high-opportunity cost disciplines like engineering and law.
(HT: Greg Mankiw).