Maybe one reason female professionals in the nonprofit sector make less than their male peers can be traced back to the volunteer work that women have contributed to social service organizations over the past couple of centuries.

In recent decades, women have achieved more powerful and prestigious roles at nonprofits. Their wages just never caught up.

That's one theory proposed by Teresa Odendahl, an author, researcher and nonprofit executive who will address the gender gap today at events sponsored by the Bayer Center for Nonprofit Management at Robert Morris University.

The Bayer Center is conducting a foundation-funded project, "74 Percent: Exploring the Lives of Women Leaders in Nonprofit Organizations," as an effort to explore why women's earnings trail men's and how to reduce the disparity.

In a study released in early 2011, the Bayer Center reported that women account for 74 percent of the approximate 300,000 people employed by nonprofits in southwestern Pennsylvania and hold 56 percent of the executive positions. But the female executive directors earned an average $89,354 annually compared with an average $118,652 for their male counterparts.

At a meeting this morning at the Omni William Penn Hotel, Ms. Odendahl will address members of the Bayer Center's "Kitchen Cabinet" -- a group of 150 women and a sprinkling of men who represent corporate, academic, nonprofit, volunteer and government sectors, and who were convened to assist with the 74 Percent project.

From noon to 2 p.m. she will appear at a lunch at the Allegheny HYP Club that is open to the public.

In a 1994 book that she co-edited, "Women & Power in the Nonprofit Sector," Ms. Odendahl put forth the hypothesis that employment in the nonprofit sector has always been dominated by women. Take for example, Jane Addams, a pioneer in the field of social work who opened the Hull House settlement in Chicago in 1889 to provide services such as medical, legal and child care for the poor and immigrants.

Nonprofit work "is gendered female," Ms. Odendahl said in a telephone interview. "It grew from an extension of work in the family and a lot of work done in the sector is still thought of as women's work. For whatever cultural reasons, that work is undervalued in our society."

When she started researching the book about 20 years ago, women earned an average 59 cents for every dollar earned by men, said Ms. Odendahl. Nationwide, that figure has risen to 82 cents on the dollar, she said citing a report from the Institute for Women's Policy Research in Washington, D.C.

But pay for female executives of nonprofits still lags men's at a national average of 69 percent of male salaries, she said. "Strangely, the more demanding the occupation and the higher skill and education required, the greater the wage disparity."

A dearth of good data makes it difficult to determine why women's paychecks are still smaller, she said. Since conducting her own research in the 1990s, "I'm sorry to say, there's been little done to update it."

Ms. Odendahl, 58, is chief executive and executive director of the Global Greengrants Fund in Boulder, Colo. The fund's grants promote environmental sustainability and social justice mainly in emerging regions such as Africa and India.

Her prior work includes executive roles at several foundations and positions with the Georgetown University Public Policy Institute, Yale University's Program on Nonprofit Organizations, and the University of California, San Diego, Women's Studies Program.

She also wrote the 1990 book, "Charity Begins at Home: Generosity and Self-Interest Among the Philanthropic Elite."

Besides discussing the nonprofit wage gap at her Pittsburgh appearances, Ms. Odendahl said she will raise the issue of female board representation.

Women occupy about 43 percent of nonprofit board seats nationwide, she said. While that number has increased since the early 1990s, "You would hope for 50 percent" by now.

"This issue is still that women tend to serve on local boards and organizations with lower budgets and staffs. The more prestigious boards with the largest budgets are still dominated by men, especially in the position of chairing the board."

Among the suggestions she has for women in the nonprofit sector, "You need to find men as allies.

"When I was doing my dissertation research in the late 1970s, I found women were trying to dress for success and networking with other women. I found your career would not advance as much if you were networking only with women. You needed to network with people with power: men."

Also, women need to be better negotiators, she said.

"If we are wanted for a job, we should demand the salary men would get for the job. We should not sell ourselves short."

Also today, the 74 Percent project plans to launch a new study of nonprofit workers that will attempt to find out the kinds of experiences they've had in the workplace. An electronic survey will be sent to 10,000 people, both men and women, mainly in the Pittsburgh region but also to some in other parts of the U.S., said Darlene Motley, associate dean of the School of Business at Robert Morris and primary researcher for 74 Percent.

Among the questions it asks are why participants chose to work in nonprofits, if they have had professional mentors, whether they have been promoted and whether they've had opportunities to negotiate salaries.

"Part of the goal here is to make it broader than just wages," said Ms. Motley. "There are things we think we can do based on what people say about mentoring, negotiation ... actual career development."

First Published: May 17, 2012, 8:00 a.m.