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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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NO.PZ2018122701000033 问题如下 Basel II requires a backtest of a bank’s internal value risk (VaR) mol (IMA). Assume the bank’s ten-y 99% Vis $1 million (minimum of 99% is harwireper Basel). The null hypothesis is: the Vmol is accurate. Out of 1,000 observations, 25 exceptions are observed (we sthe actuloss exceethe V25 out of 1000 observations).  (BinomiC) We will probably call the Vmol good (accurate) but we risk a Type I error. We will probably call the Vmol good (accurate) but we risk a Type II error. We will probably call the mol bad (inaccurate) but we risk a Type I error. We will probably call the mol bad (inaccurate) but we risk a Type II error. C is correct. 考点 Backtesting V解析 H0 : the Vmol is accurate. Hα: the Vmol is inaccurate.Z=x−pTp(1−p)T=25−1%×10001%×(1−1%)×1000=4.77Z=\frac{x-pT}{\sqrt{p(1-p)T}}=\frac{25-1\%\times1000}{\sqrt{1\%\times(1-1\%)\times1000}}=4.77Z=p(1−p)T​x−pT​=1%×(1−1%)×1000​25−1%×1000​=4.774.77 is larger th2.58, we rejethe null hypothesis. Therefore, the mol is bmol, anthis implies a risk of type I error. 我可以计算出Z= (x-pxT)/sqt[px(1-p)xT] = (25-1%x1000)/sqt[1x(1-1%)x1000] = 4.77 大于2.58,所以拒绝原假设,因此这是一个bmol。但是从哪判断这是Type I 还是type II risk? 看了之前的,还是不知道什么意思。

2024-10-05 14:14 1 · 回答

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