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水瓶公主 · 2023年06月30日

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NO.PZ2022062755000005

问题如下:

A risk manager is estimating the market risk of a portfolio using both the arithmetic returns with normal distribution assumptions and the geometric returns with lognormal distribution assumptions. The manager gathers the following data on the portfolio:

• Annualized average of arithmetic returns: 12%

• Annualized standard deviation of arithmetic returns: 30%

• Annualized average of geometric returns: 11%

• Annualized standard deviation of geometric returns: 41%

• Current portfolio value: EUR 5,200,000

• Trading days in a year: 252

Assuming both daily arithmetic returns and daily geometric returns are serially independent, which of the following statements is correct?

选项:

A.

1-day normal 95% VaR = 3.06% and 1-day lognormal 95% VaR = 4.12%

B.

1-day normal 95% VaR = 3.57% and 1-day lognormal 95% VaR = 4.41%

C.

1-day normal 95% VaR = 4.12% and 1-day lognormal 95% VaR = 3.57%

D.

1-day normal 95% VaR = 4.46% and 1-day lognormal 95% VaR = 4.49%

解释:

中文解析:


1-day normal 95% VaR = -[(0.12/252)-1.645*0.30/sqrt(252)] = 3.06%

1-day lognormal 95% VaR = 1-exp[(0.11/252)-0.41*1.645/sqrt(252)] = 4.12%

log normal的VAR的e的指数不用绝对值。

1 个答案

李坏_品职助教 · 2023年06月30日

嗨,爱思考的PZer你好:


题目问的是:正态分布下的1天的VAR和对数正态分布下的1天的VAR分别是多少。

首先要明确一点,普通正态分布是对称函数,你取不取绝对值,只是影响结果的正负号而已。对数正态分布不是对称函数,如果你取了绝对值,结果就错了。


正态分布下的公式:

正态分布下的VAR=1天的收益率-Z*1天的σ,求出来之后是个负数,要取绝对值。


对数正态分布下的公式:

基础班讲义里是以金额作为单位,题目里面是的计算结果是百分比,所以就不用乘以金额,直接就等于1-exp(1天的收益率-Z*1天的σ)。

当n小于0时,e的n次方是小于1的(指数函数的性质),所以1-e的n次方肯定是大于0的数,不要对n取绝对值。

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虽然现在很辛苦,但努力过的感觉真的很好,加油!

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