Scandinavia’s biggest bank has studied almost 11,000 publicly traded companies across the globe and the results are crystal clear: firms with a woman running the show perform far better than the market.

These are “solid results,” Robert Naess, the manager of $42 billion in stocks at Nordea Bank AB who designed the study, said by phone Monday.

The Nordea analysis shows that since 2009 firms that at the end of the calendar year were run by women (either as a chief executive officer or as head of the board of directors) went on to beat the benchmark index in all but one year. More specifically, those companies had a 25 percent annualized return over that time, which is more than double the 11 percent the MSCI World Index has delivered, based on equal weightings. The study included almost 400 companies over time.

“You can get a better return this way,” Naess said. “This effect can absolutely persist.”

As to why female CEOs deliver better results, the study is less clear. Naess suggests that women tend to be more conservative in their predictions, leaving more room for positive surprises. Naess also says the fact that only the very best women make it to the top means they’re just higher-caliber people than a lot of male CEOs.

Nordea isn’t just paying lip-service to the diversity argument. Naess is also ensuring the funds he oversees reflect the logic of the study. The Nordea Global Stable Equity Fund, which has returned 14 percent a year over the past half decade, is slightly overweight on companies run by a women, Naess said.

“If you analyze a company then a female top leader will be a positive factor in the total analysis,” he said.