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Cooljas · 2024年04月20日

为什么选A啊?VaR不是没有正齐次性吗?

NO.PZ2023091701000086

问题如下:

A risk manager is reviewing the benefits of diversification with her firm's board of directors She explains that if two securities have a 1-day 95% VaR of X and Y. then the 1-day 95%VaR of the combined portfolio will always be less than or equal to X+Y. Which of the following statements is consistent with the risk managers explanation.

选项:

A.The risk manager assumed that the values of the two securities are jointly normally distributed random variables. B.The risk manager assumed that the values of the two securities are uncorrelated. C.The risk manager assumed that the values of the two securities are independent and identically distributed random variables. D.The risk manager made no assumptions because VaR is a coherent risk measure. which supports her statement.

解释:



Cooljas · 2024年04月20日

写错了 是VaR没有次可加性

1 个答案

品职答疑小助手雍 · 2024年04月20日

同学你好,次可加性这种情况只可能出现在离散的var的场景里,连续的var的估计是服从次可加性的。

题目说组合的var会永远小于或等于单独的var相加。

其实就是用了波动率(同时也是var)的展开式:σ(A+B)= σA平方+σB平方+2*ρ*σA*σB。

这个展开式的基础假设就是A和B是jointly normally distributed random variables