​Employing more women brings a stock market boost, according to Morgan Stanley research on how diversity links to share prices.

Annual returns for businesses that employ the highest proportion of women were 2.8 percentage points above those for the least diverse firms over the past eight years, the report published Tuesday said.

This outperformance was a global phenomenon, despite big differences in gender equality between regions such as Europe, with nearly a third of board seats taken by women in May 2019, and Japan, with just 5%.

The report adds to growing research that shows diverse workforces improve returns, as regulators and an increasing number of investors around the world push for gender balance in the workplace. The all-male board is now a thing of the S&P 500's past after Copart Inc., the last company in the index without a female director, promoted its chief financial officer in July.

Morgan Stanley researchers examined the percentage of women employed throughout the hierarchy of almost 2,000 companies on the MSCI World index, adjusting for company sector. They found diverse companies outperformed even after controlling for size, yield, profitability and risk.

The trend was most pronounced in companies in developed Asian markets, with stocks ranked in the top third for gender equality outperforming those in the bottom third by 3.9 percentage points per year.

Japan was excluded from this result because the low proportion of female staff made it difficult to make meaningful distinctions between the most and least diverse third of companies. Still, the link held firm, with a 0.8 percentage point annual boost to returns for Japanese businesses in the top half of Morgan Stanley's gender rankings for the country.

In a sign of the difficulties in measuring diversity, only around half of the companies reported on their female managers and lower level employees. Missing data for each company was set to the average for its region and sector in Morgan Stanley's analysis.

This article was first published in Bloomberg.

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