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王垚 · 2020年09月08日

问一道题:NO.PZ2016082406000008

问题如下:

A portfolio consists of two bonds. The credit VAR is defined as the maximum loss due to defaults at a confidence level of 98% over a one-year horizon. The probability of joint default of the two bonds is 1.27%, and the default correlation is 30%. The bond value, default probability, and recovery rate are USD 1,000,000, 3%, and 60% for one bond, and USD 600,000, 5%, and 40% for the other. what is the best estimate of the unexpected credit loss (away from the ECL), or credit VAR, for this portfolio?

选项:

A.

USD 570,000

B.

USD 400,000

C.

USD 360,000

D.

USD 370,000

解释:

ANSWER: D

Here, the joint default probability matters. If the two bonds default, the loss is$1,000,000×(160%)+$600,000×(140%)=$400,000+$360,000=$760,000\$1,000,000\times\left(1-60\%\right)+\$600,000\times\left(1-40\%\right)=\$400,000+\$360,000=\$760,000.

This will happen with probability 1.27%. The next biggest loss is $400,000, which has probability of 3.00%-1.27%=1.73%

Its cumulative probability must be 100.001.27=98.73%100.00-1.27=98.73\%. This is slightly above 98%, so $400,000 is the quantile at the 98% level of confidence or higher. Subtracting the mean gives $370,000.

选%的时候,不是应该选择大一点的么?为什么不能选择760的98.7%呢?为什么还需要再算一个400的loss呢?谢谢

2 个答案

小刘_品职助教 · 2020年09月19日

同学你好,

这个概率不是问发生的概率,而是问损失小于760的概率。

两个债券同时违约之后,最大的损失就760,所以不可能有违约金额超过760了,反过来说,也就是P(违约金额<=760000)=100% 

小刘_品职助教 · 2020年09月08日

同学你好,

这道题取略大的就行。

760对应的概率是100%,而不是98.7%。

第一大违约金额是760000,P(违约金额<=760000)=100% 

第二大违约金额是400000  P(违约金额<=400000)=98.73%

按照98%的置信水平取违约金额是400000已经是谨慎性原则了。

vivian_zm · 2020年09月19日

为什么760对应的概率是100%,而不是98.7%?joint probability of default不是1.27%吗