Why do fund managers under perform?

In 1981, Rex Sinquefield became chairman of Dimensional Fund Advisors (DFA), and McQuown joined its Board of Directors. DFA further developed indexed based investment strategies and currently has $86 billion under management (as of Dec. 2005). Wells Fargo sold its indexing operation to Barclay's Bank of London, and it now operates as Barclays Global Investors; it is one of the world's largest money managers with over $1.5 trillion under management as of 2005.