Please discuss possible economic reasons for the variation in the U.S. stocks' Sharpe Ratio across time as shown in Table 6.7. In thinking through this question please recall our discussion of sources of investment risks.

Table 6.7 Average annual return on stocks and 1-month T-bills; standard deviation and Sharpe ratio of stocks over time Table 6.7 Average annual return on stocks and 1-month T-bills; standard deviation and Sharpe ratio of stocks over time