The 'Hillary Moment' Can Find Its Roots In Big Business

History has been made.

After last week’s primary victories in California, New Jersey and New Mexico, Hillary Clinton has all but clinched a history-making presidential nomination from a major political party when Democrats convene next month.

On a smaller scale, Clinton’s journey from her first widely known role as First Lady 20 years ago to seeking the Oval Office for herself is remarkable enough. Yet Clinton was quick to place her success in historical context, telling her supporters last week: “we all owe so much to those who came before, and tonight belongs to all of you.”

It’s also significant considering that women have only had the right to vote for fewer than 100 years – and that broad support for a female candidate is a relatively new development. In 1937, for example, Gallup polled U.S. citizens on the question of whether people would vote for a female candidate for president if she was qualified in every other respect. Sixty-four percent said no.

Amazingly, the first poll that finally saw majority support for a theoretical female candidate didn’t come until 1971, when the women’s rights moment had been growing in strength for several years.

Are women in high places delivering results?

What politics has been slow in accomplishing, though, has not been the case in the culture and hiring practices of large U.S. businesses, where female CEOs are more common than in politics. In fact, two companies in the Dow Jones Industrial Average – E I Du Pont De Nemours And Co DD and International Business Machines Corp. IBM – are led by women, and perhaps it’s some sign of progress that former HP Inc HPQ CEO and presidential candidate Carly Fiorina faced some criticism for her HP tenure rather than being subject to a politically correct “kid gloves” evaluation that is often perceived to be given to female executives.

For investors, an occasional question with female-led companies has been whether there’s any reason to think that owning these stocks is a good move on its face. That is, do stocks of companies led by women outperform those led by men?

It’s a tricky question, one that is limited by the unfortunate small sample size of women CEOs, as well as the eventual rabbit hole of trying to suss out any causal relationships. That said, a study by Fortune two years ago showed that Fortune 1000 companies with female CEOs record better stock market returns than those with male CEOs. Only 51 of the Fortune 1000 companies are run by women.

Other investments in female-led companies have also shown periods of outperformance. The No Glass Ceilings motif, for example, has increased 6.1 percent in the past 12 months. In that same time frame, the S&P 500 has gained 0.1 percent.

In the past month, the motif is up 0.1 percent; the S&P 500 is up 1.6 percent.

Other measures of the impact of having a woman in the top job are less murky. One study of 1,000 U.S. corporate boardrooms released last week showed that when women hold key leadership posts like chief executive officer or board chairman, more than 27 percent of director seats are held by women, compared with less than 18 percent when men are in charge.

Yet a recent study by Morgan Stanley scored companies on a gender-diversity ranking – not just by how many women were in leadership roles (of all kinds), but also whether it had created progressive policies on things like day care.5 The study found that American and European companies with the most generous policies gender-diversity not only offered slightly higher returns in the stock market, but did so with lower volatility. The highest-ranked North American stocks beat the lowest by 2.3 percent on a monthly annualized basis in the past five years, and when adjusted for volatility, the advantage was greater.

Once again, causality is hard to pinpoint. Do stocks of diverse companies swing less because they’re more friendly towards women, or do more successful companies have progressive policies to begin with?

For investors in companies with women CEOs, it may be enough to never figure it out and continue hoping for long-term outperformance.