Equity premium puzzle
（重定向自Equity risk premium）
The equity premium puzzle refers to the phenomenon that observed returns on stocks over the past century are much higher than returns on government bonds. It is a term coined by Rajnish Mehra and Edward C. Prescott in 1985, although in 1982 Robert J. Shiller published the first calculation that showed that either a large risk aversion coefficient or counterfactually large consumption variability was required to explain the means and variances of asset returns. Economists expect arbitrage opportunities would reduce the difference in returns on these two investment opportunities to reflect the risk premium investors demand to invest in relatively more risky stocks.