An analysis of default correlations and multiple defaults

Evaluating default correlations or the probabilities of defaultby more than one firm is an important task in credit analysis,derivatives pricing, and risk management. However, default correlationscannot be measured directly, multiple-default modeling is technicallydifficult, and most existing credit models cannot be appliedto analyze multiple defaults. This article develops a first-passage-timemodel, providing an analytical formula for calculating defaultcorrelations that is easily implemented and conveniently usedfor a variety of financial applications. The model also providesa theoretical justification for several empirical regularitiesin the credit risk literature.