问题如下：
An analyst wanting to assess the downside risk of an alternative investment is least likely to use the investment’s:
选项：
A.Sortino ratio.
B.value at risk (VaR).
C.standard deviation of returns.
解释：
C is correct.
Downside risk measures focus on the left side of the return distribution curve where losses occur. The standard deviation of returns assumes that returns are normally distributed. Many alternative investments do not exhibit close-to-normal distribution of returns, which is a crucial assumption for the validity of a standard deviation as a comprehensive risk measure. Assuming normal probability distributions when calculating these measures will lead to an underestimation of downside risk for a negatively skewed distribution. Both the Sortino ratio and the value-at risk measure are both measures of downside risk.
Sortino ratio 和 Value at risk都是衡量半方差的 ，比较符合我们传统投资收益特有的收益风险特征；而standard deviation是假设服从正太分布的情况下衡量波动率，但是另类投资大多都不服从正太分布，所以不太适用于衡量另类投资收益风险，所以C正确。
downside risk是什么意思？
