Investors' concerns and pessimism grew in 2011, and with it investors' risk tolerance, according to the MFS Investing Sentiment Survey.

"Across the board, investors' concerns rose in every major category. With a growing appetite to shun risk – 29 percent will never feel comfortable investing in stocks – and consistently high cash balances, investors are determined to avoid market volatility," said William Finnegan, senior managing director and head of U.S. retail marketing for MFS. "The challenge for investors and advisors is finding a middle ground where they can feel comfortable investing, while coping with the immediate emotional concerns of today's economic challenges."

Investors surveyed throughout the year grew more concerned as the year progressed in every category of economic issues presented. Concerns over a major drop in the stock market, weakness in the global economy and legislative gridlock in Washington, D.C. increased the most out of 12 categories, from February to October.