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yuyukou · 2022年04月04日

题目信息问题

NO.PZ2018122701000033

问题如下:

Basel II requires a backtest of a bank’s internal value at risk (VaR) model (IMA). Assume the bank’s ten-day 99% VaR is $1 million (minimum of 99% is hard-wired per Basel). The null hypothesis is: the VaR model is accurate. Out of 1,000 observations, 25 exceptions are observed (we saw the actual loss exceed the VaR 25 out of 1000 observations).  (Binomial CDF)

选项:

A.

We will probably call the VaR model good (accurate) but we risk a Type I error.

B.

We will probably call the VaR model good (accurate) but we risk a Type II error.

C.

We will probably call the model bad (inaccurate) but we risk a Type I error.

D.

We will probably call the model bad (inaccurate) but we risk a Type II error.

解释:

C is correct.

考点 : Backtesting VaR

解析 :H0 : the VaR model is accurate. Hα: the VaR model is inaccurate.

Z=xpTp(1p)T=251%×10001%×(11%)×1000=4.77Z=\frac{x-pT}{\sqrt{p(1-p)T}}=\frac{25-1\%\times1000}{\sqrt{1\%\times(1-1\%)\times1000}}=4.77

As 4.77 is larger than 2.58, we reject the null hypothesis. Therefore, the model is bad model, and this implies a risk of type I error.

老师,这道题并没有提到backtesting的significance level吧,是根据通常情况,认为4.7比较大,拒绝的吧

2 个答案
已采纳答案

DD仔_品职助教 · 2022年04月05日

嗨,从没放弃的小努力你好:


在巴塞尔协议的规则下,我们的回测标准是99% 10天的VAR,意味着model是99%的model,同时回测标准也是99%的,hard-wired per Basel表示的是硬性标准硬性要求。

这道题也是经典题里的原题,在回测这一章的第二题,老师上课有详细的讲解,建议同学再回去听一下,图一。

如果不是基于巴塞尔的模型,会给出来var模型的置信区间,同时还会说回测的区间,比如经典题的第6题,如图二。



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DD仔_品职助教 · 2022年04月05日

嗨,从没放弃的小努力你好:


同学你好,

题目说明了回测是99%,在括号里,(minimum of 99% is hard-wired per Basel).巴塞尔要求的99%来进行回测,所以用的99%双尾z值2.58。

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yuyukou · 2022年04月05日

老师,括号里是指VaR的置信度,还是返回检验的置信度,我判断不了,应该如何判断。另外,hard-wired per Basel是什么意思,是官方教材里的话么?

yuyukou · 2022年04月05日

我读了几遍,还是感觉括号里的话是在解释,bank’s ten-day 99% VaR,即解释括号前的话。从内容顺序讲,第一句描述VaR,第二句说返检,符合阅读顺序

yuyukou · 2022年04月05日

巴塞尔对VaR 的置信度有要求(99%),对VaR返检的置信度没要求,所以逻辑上括号里是在解释VaR。我的疑问是,一般题目里会如何描述返检置信度?

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