Analysts and investors have many explanations, including worries about the health of the U.S. economy and shifts in the value of the Japanese yen. Banking and Financial Institutions, Stocks and Bonds, Computers and the Internet, United States Economy, Standard & Poor’s 500-Stock Index, Currency, Interest Rates, Credit and Debt, Foreign Investments, Yen (Currency), Bank of Japan, Federal Reserve System, Japan, United States Analysts and investors have many explanations, including worries about the health of the U.S. economy and shifts in the value of the Japanese yen. NYT > Business