Read more: Buffett says $100 billion wasted trying to beat market

A passive strategy would have resulted in dramatically lower net returns over the past 30 years, diminishing the endowment’s ability to support the University, Yale said.

“Such strategies make sense for organizations lacking the resources and capabilities to pursue successful active management programs, a group that arguably includes a substantial majority of endowments and foundations,’’ according to the report. “However, Yale has demonstrated its ability to identify top-tier active managers that consistently generate better than-market returns, after considering performance fees.’’

If Yale’s assets had been invested for the past 30 years in a portfolio comprised 60 percent of U.S. equities and 40 percent of U.S. bonds, the fund would’ve been smaller, reducing by more than $28 billion the support to its educational mission, the report said.

‘Slow Rabbit’

Relative to a 90/10 portfolio, “Buffett’s personal choice,’’ Yale added $26.4 billion over the past three decades, according to the report. About one-third of Yale’s operating budget, including professor salaries and financial aid, comes from endowment income.

“While critics might argue that the classic 60/40 portfolio is a ‘slow rabbit,’ easy to beat, endowments must diversify to weather storms, such as those experienced in 1987, 1998 and 2008,’’ according to the report.

“Strong active management contributes to Yale’s outstanding absolute and relative investment performance,” the authors wrote. “While passive investment strategies result in low-fee payments, an index approach to managing the University’s Endowment would shortchange Yale’s students, faculty and staff, now and for generations to come.’’

Parents of Yale undergraduate students with annual incomes of less than $65,000 and typical assets aren’t asked to pay, and families with incomes of $200,000 and sometimes more also receive aid on a sliding scale.

Yale’s annualized 10-year returns for the year ended June 30 were 8.1 percent, behind schools including Bowdoin at 8.5 percent, Massachusetts Institute of Technology, 8.3 percent, and Princeton, 8.2 percent. Those schools are led by chief investment officers who have worked for Swensen.