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Granularity adjustment for Basel II

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  • Lütkebohmert, Eva
  • Gordy, Michael B.

Abstract

The credit value-at-risk model underpinning the Basel II Internal Ratings-Based approach assumes that idiosyncratic risk has been diversified away fully in the portfolio, so that economic capital depends only on systematic risk contributions. We develop a simple methodology for approximating the effect of undiversified idiosyncratic risk on VaR. The supervisory review process (Pillar 2) of the new Basel framework offers a potential venue for application of the proposed granularity adjustment (GA). Our GA is a revision and extension of the methodology proposed in the Basel II Second Consultative Paper. The revision incorporates some technical advances as well as modifications to the Basel II rules since the Second Consultative Paper of 2001. Most importantly, we introduce an ?upper bound? methodology under which banks would be required to aggregate multiple exposures to the same underlying obligor only for a subset of their obligors. This addresses what appears to be the most significant operational burden associated with any rigorous assessment of residual idiosyncratic risk in the portfolio. For many banks, this approach would permit dramatic reductions in data requirements relative to the full GA.

Suggested Citation

  • Lütkebohmert, Eva & Gordy, Michael B., 2007. "Granularity adjustment for Basel II," Discussion Paper Series 2: Banking and Financial Studies 2007,01, Deutsche Bundesbank.
  • Handle: RePEc:zbw:bubdp2:5353
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    References listed on IDEAS

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    1. Hashem Pesaran & Davide Pettenuzzo & Allan Timmermann, 2007. "Learning, Structural Instability, and Present Value Calculations," Econometric Reviews, Taylor & Francis Journals, vol. 26(2-4), pages 253-288.
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    Cited by:

    1. Sebastian Ebert & Eva Lütkebohmert, 2009. "Improved Modeling of Double Default Effects in Basel II - An Endogenous Asset Drop Model without Additional Correlation," Bonn Econ Discussion Papers bgse24_2009, University of Bonn, Germany.
    2. repec:wsi:ijtafx:v:20:y:2017:i:08:n:s0219024917500509 is not listed on IDEAS
    3. Klaus Duellmann & Martin Erdelmeier, 2009. "Crash Testing German Banks," International Journal of Central Banking, International Journal of Central Banking, vol. 5(3), pages 139-175, September.
    4. Gürtler, Marc & Hibbeln, Martin & Vöhringer, Clemens, 2007. "Measuring concentration risk for regulatory purposes," Working Papers IF26V4, Technische Universität Braunschweig, Institute of Finance.
    5. Yong Kim, 2013. "Modeling of commercial real estate credit risks," Quantitative Finance, Taylor & Francis Journals, vol. 13(12), pages 1977-1989, December.
    6. Christian Gourieroux & Wei Liu, 2009. "Control and Out-of-Sample Validation of Dependent Risks," Journal of Risk & Insurance, The American Risk and Insurance Association, vol. 76(3), pages 683-707.
    7. Sanjiv Das, 2007. "Basel II: Correlation Related Issues," Journal of Financial Services Research, Springer;Western Finance Association, vol. 32(1), pages 17-38, October.
    8. Tarashev, Nikola, 2010. "Measuring portfolio credit risk correctly: Why parameter uncertainty matters," Journal of Banking & Finance, Elsevier, vol. 34(9), pages 2065-2076, September.
    9. Christian Schmieder & Maher Hasan & Claus Puhr, 2011. "Next Generation Balance Sheet Stress Testing," IMF Working Papers 11/83, International Monetary Fund.
    10. Nikola Tarashev & Haibin Zhu, 2008. "Specification and Calibration Errors in Measures of Portfolio Credit Risk: The Case of the ASRF Model," International Journal of Central Banking, International Journal of Central Banking, vol. 4(2), pages 129-173, June.
    11. Mager, Ferdinand & Schmieder, Christian, 2008. "Stress testing of real credit portfolios," Discussion Paper Series 2: Banking and Financial Studies 2008,17, Deutsche Bundesbank.
    12. Gourieroux, C. & Jasiak, J., 2012. "Granularity adjustment for default risk factor model with cohorts," Journal of Banking & Finance, Elsevier, vol. 36(5), pages 1464-1477.
    13. Nikola A. Tarashev & Haibin Zhu, 2007. "Modelling and calibration errors in measures of portfolio credit risk," BIS Working Papers 230, Bank for International Settlements.

    More about this item

    Keywords

    Basel II; granularity adjustment; value-at-risk; idiosyncratic risk;

    JEL classification:

    • G28 - Financial Economics - - Financial Institutions and Services - - - Government Policy and Regulation
    • G31 - Financial Economics - - Corporate Finance and Governance - - - Capital Budgeting; Fixed Investment and Inventory Studies

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