It may be that the notorious "glass ceiling" is actually a glass door, but one that women can open only after other women have already done so, says new research by a professor at Cornell University's Johnson Graduate School of Management.

Researchers found that even a small increase in the number of women who have passed through that door to a managerial position dramatically increases other women's chances of being hired or promoted into that position. The result: a Catch-22 situation with important implications for the movement of women into management, as well as for the national affirmative action debate.

"Previous research led us to expect that a firm's gender composition -- the number of women and men at various levels in the corporate hierarchy -- would have effects on subsequent hiring and promotion patterns," said Heather Haveman, associate professor of organizational behavior at Cornell's Johnson School.

"What was startling was just how greatly the proportion of women already at the level of the job being filled mattered to the likelihood that a woman got that job. Our research shows that women had a reasonable chance to be hired or promoted into executive positions only when other women already held similar positions."

Haveman and her colleagues found that a 33 percent increase in the proportion of women at the level of the job being filled, for example, led to a 77 percent increase in the probability of a woman being promoted to that job. This was true regardless of whether a firm had many or only a few female employees at those management levels. "Clearly, the presence of women at a particular level in management ranks generates more women at that level," Haveman said. The study also found that, contrary to common wisdom, neither the number of women at levels above the position being filled (who have been seen as mentors, advocates or role models) nor the number of women below the position being filled (who constitute the promotion pool) had strong effects on the chances of a woman being hired or promoted to that position. The study, "And Then There Were More: The Effect of Organizational Sex Composition on the Hiring and Promotion of Women," examined the gender composition of managerial employees -- from assistant vice president to chairperson of the board and chief executive officer -- in the California savings and loan industry between 1975 and 1987. Lisa E. Cohen of the University of California at Berkeley and Joseph P. Borschak of the University of Texas at Austin co-authored the study.

The study found that women were more likely than men to be hired and promoted to mid- and low-level management jobs -- such as vice president, assistant vice president, secretary, treasurer and comptroller -- positions where there were already significant numbers of women. But they were far less likely than men to be hired or promoted to top-level executive positions, such as president, chief executive officer and senior executive vice president -- positions where women were scarce.

"This research offers strong support for the notion that sex segregation in managerial ranks is resistant to change. Jobs at different levels in corporate hierarchies are still typed as 'men's jobs' or 'women's jobs,'" Haveman said. "Until a significant number of women hold a particular position, it's not viewed as a job that women do. While women have made some inroads into management ranks, they are still largely absent from many management jobs -- those at the top and in functions such as finance and production. Since women aren't present in those jobs in large numbers, those jobs are typed as men's jobs, and this sex-typing blocks women from entering those jobs."

The study's findings have important implications for the country's affirmative action policies, which increasingly are being called into question.

"The obvious dilemma is: if you must have women in managerial positions for other women to move into similar positions, how do women get there in the first place?" Haveman asked. "Historically, the standard employment practices that create sex segregation in a firm -- hiring, promotion and turnover - - continue over time and replicate these patterns. This study suggests that if society values equality -- if we want women as well as men to be managers -- then we're going to need outside intervention to get the process started. Affirmative action policies that require corporations to conduct employment searches that go beyond their standard practices are one such intervention. Such policies provide the initial impetus to get women where they weren't before.. Once some women are working in high-level management jobs, say as executive vice presidents or CEOs, then those jobs cease to be typed as solely men's jobs, and other women have a reasonable chance to be hired or promoted into them."