As of October 7 -
"The S&P 500 slid 60.66 points, or 5.7 percent, to 996.23, extending its 2008 tumble to 32 percent in the market's worst yearly slump since 1937. The Dow Jones Industrial Average dropped 508.39, or 5.1 percent, to 9,447.11, giving it a 29 percent retreat in 2008 that would also be the worst in 71 years."
"The S&P 500's 15 percent retreat since Sept. 30 is the third-steepest five-day drop on record, according to Bespoke Investment Group LLC, a Harrison, New York-based research firm. The bigger slumps occurred in 1932."
Bloomberg.com: Worldwide