Trading is Hazardous to Your Wealth: The Common Stock Investment Performance of Individual Investors
Journal of Finance, 2000

Individual investors who hold common stocks directly pay a tremendous performance penalty for active trading. Of 66,465 households with accounts at a large discount broker during 1991 to 1996, those that traded most earned an annual return of 11.4 percent, while the market returned 17.9 percent. The average household earned an annual return of 16.4 percent, tilted its common stock investment toward high-beta, small, value stocks, and turned over 75 percent of its portfolio annually.

Overconfidence can explain high trading levels and the resulting poor performance of individual investors. The central message in this study by Professor Brad Barber and co-author Terrance Odean from U.C. Berkeley is that trading is hazardous to your wealth.