(Bloomberg News) Private-equity firms that are diverse or minority-owned achieved higher gains than the broader industry, according to a report today by the National Association of Investment Companies.

Funds managed by NAIC member firms, 79 percent of which are owned by minorities and 69 percent of which have women or minorities in at least half of the investment roles, had a median net internal rate of return of 15 percent from 1998 to 2011, compared with 3.7 percent for the U.S. private-equity industry, according to the report. The firms produced a median 1.5 times invested capital versus 1.1 for the industry, according to the study, which was managed by the audit and advisory company KPMG LLP.

NAIC's 27 members include Credit Suisse Group AG's customized-funds unit, Bank of America Merrill Lynch Capital Access Partners, Palladium Equity Partners LLC and Vista Equity Partners LLC, the report says. The group, whose members during the 1998 to 2011 period oversaw assets ranging from $100 million to $2.5 billion, doesn't include any of the 10 largest so-called alternative-asset firms, such as Blackstone Group LP, Carlyle Group LP and KKR & Co.

"The lack of diversity throughout the financial-services industry is reminiscent of the days when baseball owners denied that there were qualified minority ball players, or the days when professional women were relegated to the secretarial pool," Connecticut State Treasurer Denise Nappier said in a statement commenting on the report's findings. Nappier oversees the management and investment of her state's $25 billion pension fund.

At nine of those 10 biggest private-equity firms industrywide, women account for an average 8.1 percent of managing directors and senior executives, the highest-ranking and best-paying jobs, according to data compiled by Bloomberg from the companies and their websites. The comparable figure for the country's six biggest investment and commercial banks is 30 percent. Women make up 13 percent of the senior ranks at 10 of the largest traditional-asset managers.

NAIC firms oversee about 0.2 percent of the private-equity industry's assets under management, according to the group. The NAIC report is a "call to action for institutional investors everywhere that have yet to fully embrace diversity as a factor when seeking to do business," said Connecticut's Nappier.

A report published in August by the Credit Suisse Research Institute found that companies with women on their boards rewarded shareholders with corporate performance and share-price returns that are more stable than those at comparable companies with all-male boards. Net income growth at companies with female board representation averaged 14 percent over the past six years, compared with 10 percent at those without a female director, according to the study.