论文标题
强调动态损失模型
Stressing Dynamic Loss Models
论文作者
论文摘要
压力测试,尤其是反向压力测试,是风险管理实践中的重要练习。与(正向)应力测试相比,反向应力测试旨在找到一个替代但合理的模型,以便在替代模型下,特定的不良应力(即约束)得到满足。在这里,我们为动态模型提出了反向应力测试框架。具体而言,我们在有限的时间范围内考虑了复合泊松过程,并由终端时间应用于该过程的函数的预期值组成。然后,我们将应力模型定义为该过程满足约束的概率度量,并最大程度地减少Kullback-Leibler差异与参考复合泊松模型。 我们解决了这一优化问题,证明了应力概率度量的存在和独特性,并提供了从参考模型到应力模型的ra子 - 尼克比衍生物的表征。我们发现,在压力度量,过程的强度和严重程度分布取决于时间和状态。我们通过考虑VAR以及VAR和CVAR的应力来说明动态应力测试,并提供了在这些应力下如何改变随机过程的例证。我们将框架概括为多变量复合泊松过程和应力,而这些过程和应力有时是除终端时间以外的。我们通过考虑``如果''方案,回答一个问题来说明框架的适用性:在较早的时候,在投资组合组件上压力的严重程度是什么,以使总投资组合超过终端时间的风险阈值?此外,对于一般的约束,我们提出了一种算法来模拟应力度量下的样本路径,从而可以比较应力对过程动力学的影响。
Stress testing, and in particular, reverse stress testing, is a prominent exercise in risk management practice. Reverse stress testing, in contrast to (forward) stress testing, aims to find an alternative but plausible model such that under that alternative model, specific adverse stresses (i.e. constraints) are satisfied. Here, we propose a reverse stress testing framework for dynamic models. Specifically, we consider a compound Poisson process over a finite time horizon and stresses composed of expected values of functions applied to the process at the terminal time. We then define the stressed model as the probability measure under which the process satisfies the constraints and which minimizes the Kullback-Leibler divergence to the reference compound Poisson model. We solve this optimization problem, prove existence and uniqueness of the stressed probability measure, and provide a characterization of the Radon-Nikodym derivative from the reference model to the stressed model. We find that under the stressed measure, the intensity and the severity distribution of the process depend on time and state. We illustrate the dynamic stress testing by considering stresses on VaR and both VaR and CVaR jointly and provide illustrations of how the stochastic process is altered under these stresses. We generalize the framework to multivariate compound Poisson processes and stresses at times other than the terminal time. We illustrate the applicability of our framework by considering ``what if'' scenarios, where we answer the question: What is the severity of a stress on a portfolio component at an earlier time such that the aggregate portfolio exceeds a risk threshold at the terminal time? Furthermore, for general constraints, we propose an algorithm to simulate sample paths under the stressed measure, thus allowing to compare the effects of stresses on the dynamics of the process.