While higher education worries about undergraduate student bodies lacking a good ratio of men, that's not a problem in college board rooms, which remain dominated by men.

But a new national survey of four-year colleges and universities finds slow but steady progress in the representation of women on college boards. Between 1981 and 2007, the percentage of trustees who are women increased to 31 percent from 20 percent.

The percentage of female board chairs during that time increased to 18 percent from 10 percent.

The study was conducted for the Association of Governing Boards of Colleges and Universities and analysis was released by the Cornell Higher Education Research Institute. A paper on the research -- by Ronald G. Ehrenberg, director of the center, and Joyce B. Main, a Ph.D. student at Cornell -- notes that future research will explore whether there is a link between the share of female trustees and efforts by colleges to recruit and retain greater numbers of female faculty members.

Female trustees -- especially in powerful roles on boards -- were once relatively rare. A report on female trustees at the University of Pennsylvania notes that when Judith Rodin became Penn's first female president in 1994, she was only the ninth woman to serve on the board's Executive Committee -- and Penn was chartered in 1755. At many colleges and universities, board chairs who are women are the first to hold that role, and it is considered notable enough to issue a press release. Adrian College and Johns Hopkins Universities are among the institutions that have only recently named a woman as board chair.

The Cornell paper on the data notes that much of the research about corporate boards and gender suggests that women tend to have an impact, not when there are only one or two female board members, but when there is some critical mass. The research found that the share of boards with at least three female members rose to 90 percent from 60 percent over the years studied. The number of boards with at least five female members rose to 60 percent from 40 percent.

In terms of gender representation on boards, the study did not find notable differences between public and private institutions. Comparing bachelor's, master's and doctoral institutions, the study found increases in female representation on boards across the sectors. However, the proportion of female trustees is lowest at doctoral institutions.