(Bloomberg News) The Standard & Poor's 500 Index may slump as much as 21 percent as volatility on the benchmark measure continues, according to Bank of America Corp. technical analysts.

The U.S. benchmark index may slump to 910, Mary Ann Bartels and Stephen Suttmeier, Bank of America's New York-based technical market analysts, wrote in a report today. That would be 21 percent lower than the index's closing price of 1,154.23 on Sept. 9.

"We are more concerned now that the downside risk could be more than we originally forecast," Bartels and Suttmeier wrote. "Measured moves suggest 985-910 on the S&P 500 is a potential range where a market bottom may finally be found."

The VIX, as the Chicago Board Options Exchange Volatility Index is known, jumped 14 percent to 38.52 last week, as concern Greece's finances are deteriorating overshadowed President Barack Obama's $447 billion plan to stimulate growth. The gauge measures the cost of derivative prices on the S&P 500.

"We expect several more months of volatility and once a bottom is made it will take months to build a base to repair the equity market -- this could carry over into 2012," Bartels wrote. "The violent swings within the market are more typical of a bear market than a bull market. We suggest using rallies to raise cash and or become more defensive until our trip wire to a bottom generates a buy signal."

In technical analysis, investors and analysts study price graphs to predict changes in a security, commodity, currency or index.