The Jarrow–Turnbull credit risk model was published by Robert A. Jarrow of Kamakura Corporation and Cornell University and Stuart Turnbull, currently at the University of Houston.[1] Many experts in financial theory label the Jarrow–Turnbull model as the first "reduced-form" credit model. Reduced-form models are an approach to credit risk modeling that contrasts sharply with the "structural credit models".[2] The structural or "Merton" credit models are single-period models which derive the default probability from the random variation in the unobservable value of the firm's assets. Two years after the development of the structural credit model, Robert Merton modeled bankruptcy as a continuous probability of default.[3] Upon the random occurrence of default, the stock price of the defaulting company is assumed to go to zero. Merton derived the value of options for a company that can default. This was in fact the first "reduced form" model where bankruptcy is modeled as a statistical process, rather than as a microeconomic model of the firm's capital structure.
The Jarrow–Turnbull model extends the reduced-form model of Merton (1976) to a random interest rates framework.
Large financial institutions employ default models of both the structural and reduced form types. The Merton structural default probabilities were first offered by KMV LLC in the early 1990s. KMV LLC was acquired by Moody's Investors Service in 2002. Kamakura Corporation, where Robert Jarrow serves as director of research, has offered both structural and reduced form default probabilities on public companies since 2002.