U.S. stocks fell this week, sending the Dow Jones Industrial Average to the biggest loss since 2008, as the Federal Reserve said risks to the economy have increased and concern grew that policy makers will fail to spur growth.

Equities rebounded today, following a four-day rout that erased $1.1 trillion in value, amid speculation governments will act to prevent a financial crisis. For the week, Alcoa Inc. and DuPont Co. tumbled more than 14 percent to lead losses in the Dow. Materials companies in the Standard & Poor’s 500 Index slipped 12 percent for the biggest drop among 10 industries as every group declined at least 1.6 percent. Bank of America Corp. slumped 13 percent, while FedEx Corp. tumbled 12 percent.