U.S. Department of Education, about 45 percent of all faculty members were in part-time jobs in 2001. Another 19 percent held full-time, non-tenure-track jobs.

Those professors earn far less money than their full-time, tenure-track colleagues, but figuring out exactly how to compare the different categories is difficult, and comprehensive statistics on part-timers' salaries are not available.

The AAUP report uses a recent study by James W. Monks, an assistant professor of economics at the University of Richmond, to highlight the gap. Mr. Monks used data from the Department of Education's 1999 National Study of Postsecondary Faculty to examine professors' pay, and he based his study on salary per hour to adjust for the extra responsibilities that full-time professors have, such as research and service.

Mr. Monks found that full-time, non-tenure-track professors earn 26 percent less than comparable full-time, tenure-track assistant professors. The gap for part-timers was even wider. According to Mr. Monks's analysis, they earn 64 percent less per hour.

Mr. Monks was a contingent faculty member before landing his tenure-track job at Richmond. He served as a visiting professor for three years at Mount Holyoke College and later taught as an adjunct at Wellesley College. While he acknowledges that not every adjunct eventually gets a tenure-track position, he says research on such professors is lacking. "Am I in the half who made it? Or am I in the 10 percent who made it?" he says. "We don't know the life cycle of the contingent faculty."

Gender Equity

The AAUP report presents several indices to examine how female faculty members have fared compared with male faculty members over the past two decades. For instance, despite gains at doctoral institutions, full-time female professors are still outnumbered two to one there. In contrast, they now make up a slight majority at two-year institutions.

Salaries for men and women at community colleges are now nearly equitable, according to the report. But female professors at doctoral institutions, on average, earn about 80 percent of what their male counterparts make.

The report notes that differences in discipline and highest degree earned may explain some salary differentials. "But such an 'explanation' -- used often in the statistical sense of 'explaining variance' -- really begs further questions," the report says. "Why is it that the disciplines in which women faculty predominate tend to be lower paid? Why are women faculty less likely to hold doctorates? ... Why might women be more likely than men to have interrupted their academic careers?"