The Two Defaults Scenario for Stressing Credit Portfolio Loss Distributions

Journal of Risk and Financial Management 9(1), 1-18, 2016

20 Pages Posted: 1 Nov 2015 Last revised: 7 Jan 2016

See all articles by Dirk Tasche

Dirk Tasche

Swiss Financial Market Supervisory Authority (FINMA)

Date Written: October 27, 2015

Abstract

The impact of a stress scenario of default events on the loss distribution of a credit portfolio can be assessed by determining the loss distribution conditional on these events. While it is conceptually easy to estimate loss distributions conditional on default events by means of Monte Carlo simulation, it becomes impractical for two or more simultaneous defaults as then the conditioning event is extremely rare. We provide an analytical approach to the calculation of the conditional loss distribution for the CreditRisk portfolio model with independent random loss given default distributions. The analytical solution for this case can be used to check the accuracy of an approximation to the conditional loss distribution whereby the unconditional model is run with stressed input probabilities of default (PDs). It turns out that this approximation is unbiased. Numerical examples, however, suggest that the approximation may be seriously inaccurate but that the inaccuracy leads to overestimation of tail losses and hence the approach errs on the conservative side.

Keywords: Risk concentration, stress test, scenario analysis, joint default probability

JEL Classification: G11, C11

Suggested Citation

Tasche, Dirk, The Two Defaults Scenario for Stressing Credit Portfolio Loss Distributions (October 27, 2015). Journal of Risk and Financial Management 9(1), 1-18, 2016, Available at SSRN: https://ssrn.com/abstract=2684801 or http://dx.doi.org/10.2139/ssrn.2684801

Dirk Tasche (Contact Author)

Swiss Financial Market Supervisory Authority (FINMA) ( email )

Einsteinstrasse 2
Bern, 3003
Switzerland

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