U.S. investors who sold stocks in their retirement accounts during market volatility in 2008 and 2009 did worse than those who stayed in stocks, according to Fidelity Investments.

Participants in 401(k) savings plans who dumped stocks from Oct. 1, 2008 to March 31, 2009, when the S&P 500 Index fell 31 percent, and hadn’t returned to stocks as of June 30, 2011 had an average account balance increase of only 2 percent, according to the study released today. Those who maintained some stock allocation during that period saw their balances rise 50 percent on average.

“Staying the course does prove to be an effective strategy in the long term,” said Beth McHugh, vice president of market insights for Fidelity Investments. “Any move can have a dramatic long-term effect.”

[source: Bloomberg]