A New Framework for Measuring the Credit Risk of a Portfolio: The "ExVaR" Model

This paper proposes a new framework for the quantitative evaluation of the credit risk of a portfolio by extending the concept of value at risk. In practice, the risk evaluation period is set individually for each transaction in the portfolio and a simulation is carried out on the movements of default probabilities, interest rates, and collateral asset prices as well as on the realization of defaults of counter parties. The result fixes the cash flow along the simulated path and leads to the present value of the total cash flows. By repeating this procedure many times, we obtain the probability distribution of the present value, by which we can evaluate the price and the risk of the portfolio. This framework enables us comprehensively and objectively to measure the risk taking into account the diversification/concentration effect, the collateral effect, and the correlation between credit risk factors and market risk factors. After presenting the methodology, the paper calculates the risk of hypothetical test portfolios. They are used to discuss the applicability of the framework to practical uses.