the coefficient variation of the S&P is Table 24 Arithmetic Mean Annual Return and Standard Deviation of Returns, U.S. Asset Classes, 1926-2002 Arithmetic Mean Return (%) Standard Deviation of Return (%) Asset Class 12.3 21.9 35.1 16.9 S&P 500 U.S. small stock U.S. long-term corporate U.S. long-term government U.S. 30-day T-bill 6.1 7.2 5.8 8.2 3.8 0.9