The good news, according to a study to be released Monday by the executive search firm Heidrick & Struggles, is that the pace of women joining boards of directors is accelerating.

Women now hold 20.2 percent of corporate board seats among Fortune 500 companies, up from 18.7 percent in 2013 and 17.2 percent in 2009, when Heidrick began tracking the number. The recruiting firm now expects women will achieve gender parity on corporate boards by 2042, 16 years earlier than the date it predicted last year. "We’re seeing some incremental pickup," says Bonnie Gwin, vice chairman and managing partner of the firm's North American board practice. "While it's still a small percentage uptick, that’s a positive."

Yet that good news is also the bad news: If the numbers are correct, it will be 28 more years before women make up 50 percent of the directors overseeing corporate managers and looking out for shareholders' interests.

Gwin, however, is optimistic that it could happen even sooner. One pivot she's seen recently is that companies are interested in adding more board members who don't have CEO experience. During the recession, companies rushed to add directors who had been public company CEOs (most of whom, of course, are men), in order to beef up top-level managerial expertise as their companies struggled with the economic morass.

Now, she says, more companies are embracing directors who have different backgrounds — general counsels with regulatory experience, chief financial officers who know M&A, marketing mavens who can help with brand strategy — far more of whom are women. "Boards are thinking more expansively about the other skills they need around the table," Gwin says.

Another encouraging sign that women could reach more board positions faster is that the percentage of women in board leadership positions is climbing. According to data from the study, roughly 8 percent of Fortune 500 companies have either a lead director, independent chairman of the board or a combined chairman-CEO who is a woman. And women comprise nearly 22 percent of the chairs of nominating and governance committees, which are responsible for picking other board members. It shows they are starting to reach some key committee leadership roles in representative numbers.

While the percentage of female Fortune 500 board leaders is still soberingly low, it's nearly twice that of female CEOs, who make up just 4.8 percent of those companies.

Finally, yet another shift Gwin highlights is that some companies have begun adding term limits, combined with age limits, to urge more turnover on the board. Currently, board turnover is extraordinarily low: On an annual basis, roughly five percent of directors tend to change seats, according to the Heidrick report. That could be one reason women have been slow to gain ground — they must wait for more men to leave. And who wants to do that? The median pay for directors is north of $200,000 a year, with many making much more through lucrative equity grants.

Term limits or higher turnover, however, may not be the greatest panacea of all. In the United Kingdom, Gwin says, turnover is more frequent since directors are no longer deemed independent once they've been on the board for nine years, yet the prevalence of women directors there is no better than in America. Among the top 100 U.K. companies, 17.3 percent of directors are women. Rather than term limits, Gwin says, "what has happened in the U.K. to increase the number of women is there has been a lot of public pressure."

So perhaps shame, rather than policy changes, could be the best motivator.

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