In a 2001 study published in the Quarterly Journal of Economics Terry Odean and Brad Barber showed that the more often folks trade, the worse they do.

FORBES: Magazine Article

In a different Forbes blog, Rick Ferri (The Indexer) mentions the work by Brad Barber ( University of California at Davis), Emmanuel George ( Ross School of Business), Reuven Lehavy ( Ross School of Business), and Brett Trueman ( Anderson School of Management).

FORBES: The Quant Idea

In a landmark study titled Boys Will Be Boys: Gender, Overconfidence and Common Stock Investment professors Brad Barber and Terrance Odean of the University of California, Davis, documented that men traded 45 percent more than women and ended up having their net returns reduced by almost a full percentage point compared to women.

FORBES: What Men Can Learn from Women to Invest More Profitably