The Basel II IRB approach revisited: do we use the correct model?

Varsanyi, Zoltan (2006): The Basel II IRB approach revisited: do we use the correct model?

Abstract

In this paper I question whether the risk weights in the advanced (IRB) approach of the Basel 2 regulation are appropriate, on a strictly theoretical ground. The major concern is that the model behind the regulation considers defaults only at the end of the time horizon for which capital is to be held - whereas defaults in the whole time interval should be taken into consideration. This latter approach is represented by a model that is different from the Basel model. It follows, as I show, that the Basel model should be viewed just as a technical tool to turn the expected value of the unconditional loss distribution into a given percentile of the same distribution - making use of conditional (on the systemic factor) default probabilities - and should not be interpreted as describing even 'virtual' firms and asset values. More importantly, I also show that a logical step in the theoretical foundation of the model is missing which raises the question whether the risk weights calculated with the model are indeed appropriate. Due to difficulties in the calculation in the alternative approach of the percentiles of the loss distribution no clean-cut answer is given in this paper.

• Item Type: MPRA Paper
• Language: English
• Keywords: Basel II; credit risk
• Subjects: G - Financial Economics > G2 - Financial Institutions and Services > G28 - Government Policy and Regulation

References

AU [2005]: 'Implementation of the Basel II Capital Framework - 3. Internal ratings-based approach to credit risk', Australian Prudential Regulation Authority, 28 July 2005 BCBS [2005]: 'An Explanatory Note on the Basel II IRB Risk Weight Functions', BIS Chhikara, R.S., Folks, J.L. [1989]: 'The Inverse Gaussian Distribution, Theory, Methodology and Applications', Marcel Dekker Inc., New York Cornford, A. [2005]: 'The Global implementation of Basel II: Prospects and Outstanding Problems', http://www.g24.org/cornfor2.pdf Gordy, M. [2002]: 'A Risk Factor Model Foundation for Ratings-Based Bank Capital Rules', Board of Governors of the Federal Reserve System HK [2004]: 'Proposals for the Implementation of the New Basel Capital Adequacy Standards ("Basel II") in Hong Kong', Hong Kong Monetary Authority, August 2004 Kamstra, M., Milevsky, M. A. [2004]: 'Waiting for Returns: Using Space-Time Duality to Calibrate Financial Diffusions', Schulich School of Business, York University, Canada SG [2004]: 'IRB Approach - Rollout & Exclusions', Monetary Authority of Singapore, August 2004