Take that, Paul Tudor Jones.

The billionaire investor controversially said last May that women can have trouble focusing on trading once they become mothers. Yet a new study released Wednesday finds that women hedge fund managers outperformed both the Standard & Poor's 500-stock index as well as a broad index of hedge funds in recent years.

The study by tax and audit firm Rothstein Kass, which serves the financial industry, found that the average women-owned or -managed hedge fund returned six percent over the 6.5 years ending June 30, 2013. Over the same period, the S&P 500 rose 4.2 percent, while the HFRX Global Hedge Fund Index dropped a little more than 1 percent.

This wasn't the first time women hedge fund leaders have been shown to outperform the market. Rothstein Kass published similar results in its 2013 study. A 2011 Barclays Capital report found that for the five years ending March 2011, a weighted index of  women- and minority-owned hedge funds returned a cumulative 82.4 percent compared with a "non-diversity" cumulative return of 51 percent. And another 2010 report, using data by Hedge Fund Research from 2000 to 2009, found that since inception the average annual return for hedge funds run by women was 9.1 percent, compared with 5.8 percent for the broad market. 

Rothstein Kass audit partner Kelly Easterling says women outperform men primarily for two reasons: their approach to risk, and the size of the funds they manage. Research has shown that women take less risk, are less likely to be overconfident and trade less often, which can add up to steadier returns. Meanwhile, because they tend to run smaller funds with fewer assets, women can move in and out of positions more readily than peers at larger funds, Easterling says. "They're able to be more nimble within their investments."

The firm's research also showed that, despite these results, few pensions or institutional investors have mandates that require them to allocate a portion of their investments into women-run funds. (While uncommon, there are some pension funds and institutional investors that have in fact instituted such mandates, in order to ensure they hold assets by emerging managers or better mirror the demographic makeup of their investors.) Still, while 93 percent of investors surveyed had no specific mandate to invest in funds run by women, 24.5 percent of respondents said they planned to increase the investments made into women-owned funds.

Improving the number of female managers at the top, Easterling says, will require women to have access to broader networks that allow them to raise capital and to hold more positions, so they can more easily build a track record that's portable. Currently, women most commonly sit in operational, financial or compliance roles in the hedge fund and private equity worlds. They hold just 22.5 percent of chief investment officer and 17.2 percent of chief executive officer positions among the firms polled.

Some good news from the research is that the number of women who say gender has hampered their success has ticked down since Rothstein Kass's last study, albeit slightly—from two-thirds in the 2013 report to 61 percent this year. Also encouraging, if marginally so, is that 17.5 percent of the 440 senior women surveyed said they have a goal of managing their own fund within the next five years, up from 14.2 percent in last year’s report.

Jena McGregor is a columnist for On Leadership.

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