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Merton for Dummies: A Flexible Way of Modelling Default Risk


  • Hans Byström


One of the most popular approaches to default probability estimation using market information is the Merton [1974] approach. By explicitly modelling a firm's market value, market value volatility and liability structure over time using contingent claims analysis the Merton model defines a firm as defaulted when the firm's value falls below its debt. In this paper we show how a simplified "spread sheet" version of the Merton model produces distance to default measures similar to the original Merton model. Moreover, when applied to a sample of US firms, the simplified model gives a relative ranking of firms that is essentially unchanged compared to the Merton model. Our paper has three main implications. First, the simplicity of our model makes it suitable as a framework for a more elaborate dynamic modelling of volatility and leverage ratios with the aim of capturing the dynamic nature of default risk suggested by empirical evidence. At the same time, in the model's most simple version, distance to default can be calculated very quickly and intuitively (on the back of an envelope). Second, the default probability's insensitivity to the leverage ration at high levels of debt makes it possible to apply the model to banks and other highly leveraged firms without exact knowledge of their leverage ratios. Third, the model can be applied to any firm regardless of its level of riskiness without estimation problems.

Suggested Citation

  • Hans Byström, 2003. "Merton for Dummies: A Flexible Way of Modelling Default Risk," Research Paper Series 112, Quantitative Finance Research Centre, University of Technology, Sydney.
  • Handle: RePEc:uts:rpaper:112

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    Blog mentions

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    1. Experts Hate Simplicity (in public)
      by Eric Falkenstein in Falkenblog on 2009-05-05 01:24:00


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    Cited by:

    1. Rodrigo Alfaro A. & Natalia Gallardo S. & Camilo Vio G., 2010. "Análisis de Derechos Contingentes: Aplicación a Casas Comerciales," Notas de Investigación Journal Economía Chilena (The Chilean Economy), Central Bank of Chile, vol. 13(1), pages 73-82, April.
    2. Rodrigo A. Alfaro & Rodrigo Cifuentes S., 2011. "Financial Stability, Monetary Policy, and Central Banking: An Overview," Central Banking, Analysis, and Economic Policies Book Series, in: Rodrigo Alfaro (ed.),Financial Stability, Monetary Policy, and Central Banking, edition 1, volume 15, chapter 1, pages 001-010, Central Bank of Chile.
    3. Byström, Hans N. E., 2005. "Credit Default Swaps and Equity Prices: The Itraxx CDS Index Market," Working Papers 2005:24, Lund University, Department of Economics, revised 15 May 2005.
    4. Muhammad Suhail Rizwan & Asifa Obaid & Dawood Ashraf, 2017. "The Impact of Corporate Social Responsibility on Default Risk: Empirical evidence from US Firms," Business & Economic Review, Institute of Management Sciences, Peshawar, Pakistan, vol. 9(3), pages 36-70, September.
    5. Rodrigo A. Alfaro. & Andrés Sagner & Carmen G. Silva, 2011. "Aplicaciones del Modelo Binomial para el Análisis de Riesgo," Working Papers Central Bank of Chile 631, Central Bank of Chile.

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