A recent report shows that investors might be wise to buy stock in companies that have female directors.

The study by market index provider MSCI, looked at more than 4,000 public companies around the world and found those with boardrooms featuring “strong female leadership” saw a 36.4% greater return on equity since the study began in 2009: 10.1% vs. a 7.4% return for the companies with a more male-dominated leadership.

MSCI defines a company as having “strong female leadership” if its board has at least three female members, or if the percentage of female directors is higher than average in the country where that company is based.

According to MSCI, its research reflects similar findings from other surveys, including one from Credit Suisse in 2014 that showed large companies with market values above $10 billion with at least one female board member outperformed companies with all-male boards by 5%.

But for investors looking to add female-centric companies to their portfolios, the pickings are slim. MSCI also found that just over 15% of the board seats at companies it tracked worldwide were occupied by women as of 2015, and about 17% among U.S. companies. Based on current trends, MSCI predicts the global percentage of female board directors is unlikely to hit 30% until 2027.

Earlier this year, Fortune reported that 23 Fortune 500 companies still had entirely male boards, while the percentage of female board directors in the Fortune 500 only grew by about 3.3% over the past decade. In addition to the potential for greater shareholder return, another recent study showed that companies with more women on their boards are also more likely to have greater racial diversity.