One way to close the pay gap for women

We haven't yet pinpointed the reason that having more female board members leads to higher pay for female executives. Some scholars argue that diversity promotes deeper discussions in the boardroom. Others say that having more females at the table reduces gender bias. Whatever the reason, the gap in gender-diverse firms is lower than at companies with all-male boards.

How do we achieve even greater board equity? The answer is not obvious. One problem is the supply. Though board members don't need to come from corporate America, many of them do. And with so few females in executive positions, there may not be enough women with high-level experience to populate those boards.

But we're getting there.

Women are reaching top jobs in all fields. Three women now hold four stars in the U.S. military. Six of the eight Ivy League universities have had female presidents.

Female lawmakers comprise more than 20% of the U.S. Congress, nearly double the level of 20 years ago. In corporate America, female executives held 9% of the top positions in S&P 1500 companies in 2014, triple what it was two decades ago. All these high-achieving women are potential board members, and greater supply yields greater placement: In 2014, almost 15% of S&P 1500 board seats were held by women, double the 1997 rate.

To be sure, not all the pay gap is rooted in unequal board representation. Our research shows that female executives tend to accept less at-risk pay — stock options and other performance-based equity compensation. They are more risk averse and prefer more certain payouts, like salary. Since equity compensation is a large part of pay, some of the gap may never disappear.

We are able to study the most highly paid executives in the United States because the Securities and Exchange Commission requires companies to disclose their compensation each year, yet even full transparency hasn't stopped corporate America from paying women less than men for the same jobs.

For S&P 1500 executives, total pay for females was 15% lower than that of their male counterparts in our 1996--2010 sample. And no matter how we slice and dice the data, the gap endures: We match each female executive with a male of the same title, age and tenure at a similar firm. What do we find? On average, she's paid less. We identify cases in which a man is replaced by a woman and vice versa and (surprise!) pay for the new executive is higher if the replacement is male and lower if female.

Over the course of a career, this is costly: An analysis from the National Women's Law Center, a nonprofit advocacy group, shows that for the average woman in the United States, such inequality reduces lifetime pay by $430,000.

Politics may have its problems but give Washington this: It mandates pay equity in elected positions. If Hillary Clinton replaces Barack Obama as president, she'll be paid the same wage.

But pay gaps exist across all other segments of the work force -- even in Hollywood and professional sports, as the actress Jennifer Lawrence and players on the U.S. women's national soccer team will tell you.

Though there is hope for pay equity in the corner office, for women in less high-profile roles, closure of the pay gap progresses at a snail's pace. After nearly a century and a half, we still have a long way to go. Happy National Equal Pay Day.

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