Yahoo CEO Marissa Mayer listens during the World Economic Forum, in Davos, Switzerland in 2013. The value of their median pay package for the relatively small number of women CEOs in the S&P 500 was actually higher than it was for their male peers. In a company filing, Mayer's 2015 package was valued at nearly $36 million, though her actual earned compensation for 2015 was a relatively smaller $13.9 million. (AP Photo/Keystone, Laurent Gillieron)

The gender pay gap is a persistent phenomenon, research shows, affecting women ranging from young female college graduates to mid-career mothers to even groups of top executives.

But look at the pay packages for the small group of women who are CEOs of the largest public corporations, and you'll find something a little different: Female CEOs appear to be keeping pace--if not out-earning--their peers.

Women at the 100 largest of those companies earned an average of $22.7 million, compared to $14.9 million for the men, according to an analysis released Friday by Equilar, the executive compensation research firm. To conduct its findings, Equilar looked at the 100 largest companies by revenue that had filed their proxy statements by April 1. Of that universe, eight companies were led by women, and six of them received a pay increase in 2015, according to the analysis.

"This is pretty consistent with what we’ve seen last year as well," said Dan Marcec, Equilar's director of content. "Obviously it’s a much smaller sample size, but the top-paid females tend to be paid pretty high." 

Expand the group to the broader Standard & Poor's 500-stock index, meanwhile, and one finds a similar trend. There are 24 current female CEOs among those 500 companies, according to data provided by S&P Capital IQ. One of them, Occidental Petroleum CEO Vicki Hollub, was just named to the job in April, so she was excluded from the wider analysis.

Among the remaining 23 women, the median pay package was valued at roughly $13 million for their most recent fiscal year, according to an analysis of data from the filings. That median is actually higher than the roughly $11 million median pay package received by their male peers. The figure for the men is based on a review of the pay packages going to more than 300 CEOs in the S&P 500, an analysis conducted by ISS Corporate Solutions, a subsidiary of proxy adviser Institutional Shareholder Services that provides research to companies.

A few notes about the analyses: They rely on totals from the "summary compensation tables" outlined in company filings, a commonly used figure in pay comparisons which represents the value of the pay package when it is granted and assumes companies meet their performance targets, even though CEOs may not be eligible for some of the included stock grants until future years. However, changes in pension values were excluded from those figures, since the calculation doesn't reflect the active decisions boards make each year. Two of the female CEOs, Oracle co-CEO Safra Catz and Campbell Soup Co. CEO Denise Morrison, lead companies that don't report their annual data during the traditional spring proxy season, so we examined their most recently reported totals.

Some pay experts were surprised by the results. "I’ll be honest, when I ran the numbers, I went in and double checked them," said Eric Hoffmann, vice president of information services at Farient Advisors, an executive pay consulting firm. "The narrative is females make less than males. While that’s true across the board, when you start to look at CEOs the dynamic changes a little bit." 

The small sample size likely plays a role. With just 23 women in the group, any average is going to be skewed by especially large packages, such as Catz's, which was valued at $53.2 million for Oracle's most recent fiscal year.

Meanwhile, some research has shown that CEOs recruited from the outside get paid more than those groomed through the ranks, and female CEOs tend to be recruited from the outside more often than men. But that doesn't appear to explain the data here: While there are examples of high-profile women who were recruited to the job--such as Yahoo's Marissa Mayer, whose 2015 package was valued at nearly $36 million--the majority of the current female CEOs were appointed from the inside, with several having long careers at the companies they now lead. (It's worth noting that $36 million figure reflects accounting and SEC rules for how pay packages are valued; Mayer's actual earned compensation for 2015, Yahoo's filing states, was a relatively smaller $13.9 million because "2015 performance fell short of the rigorous annual financial goals we set.")

Pay experts say the most likely explanation for the relatively strong showing by women is that they tended to lead some of the largest companies. Annual revenues are one of the biggest drivers in executive pay, they say. Eight of the 23 executives at S&P 500 companies fall within the top 100, and 15 of the 23 fall in the top half.

At this level, gender is less likely to figure in a board's calculations, said Hoffmann. It's certainly possible that "in order to get to the CEO role, maybe these women have to be twice as smart and twice as good, and therefore they earn more," he said. But he notes that boards of big companies tend to set pay levels for CEO based on "market data and peer groups that they're targeting irrespective of gender."

That female CEOs appear to be keeping pace with--and in some cases, even exceeding--their male peers, does not mean there isn't a gender gap in the executive suite, however. A study last year by an economist at the Federal Reserve Bank of New York, for instance, found that among top executives--not only CEOs, but chief financial officers, chief operating officers, presidents and vice chairs--the median woman in the study earned 14 percent less than her male peer. Much of that gap, the study found, can be explained by women receiving less incentive pay, bonuses and stock options or grants than their male peers.

Even then, the biggest divide at the top of corporate America isn't the pay gap, but the position gap. With only 24 women running S&P 500 companies, just under 5 percent of its CEOs are women. According to the nonprofit research firm Catalyst, just 19 percent of board seats and 25 percent of senior level managers are women. In other words, it could be a long time before that sample size issue goes away.

Read also:

Only one woman was named CEO of a major company in North America in 2015

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