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Why Ratings Matter: Evidence from Lehman's Index Rating Rule Change


Author Info

  • Zhihua CHEN

    (University of Neuch√Ętel, Shanghai University and SwissFinance Institute)

  • Aziz A. LOOKMAN

    (Moody's Investors Service)

  • Norman SCHURHOFF

    (University of Lausanne, Swiss Finance Institute and CEPR)

  • Duane J. SEPPI

    (Carnegie Mellon University)


This paper examines the role of bond ratings and the effects of rating-based regulations in the corporate bond market. Exploiting an unanticipated mechanical change in how the benchmark Lehman bond indices are constructed in 2005, we show that rating-induced market segmentation of the bond market into investment-grade and high-yield sectors has a first-order impact on bond prices. Bonds that are mechanically upgraded to investment-grade due to the Lehman announcement have positive abnormal returns of two percent on average and exhibit abnormal order flows over several months. The abnormal bond returns are larger for bonds with longer maturities and higher turnover. We find that institutional investors with rating's-based portfolo constraints substantially increase their holdings in the a ected bonds. In addition, return correlations with the investment-grade index increase for the upgraded bonds. Bonds on watch for downgrade to high-yield but with favorable Fitch rating experience reduced selling and rapid price recovery.

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Bibliographic Info

Paper provided by Swiss Finance Institute in its series Swiss Finance Institute Research Paper Series with number 10-30.

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Length: 61 pages
Date of creation: Jun 2010
Date of revision:
Handle: RePEc:chf:rpseri:rp1030

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Related research

Keywords: Corporate bond market; rating agencies; rating-based regulation; market segmentation; liquidity; index addition; institutional investors;

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Cited by:
  1. Bo Becker & Todd Milbourn, 2010. "How did increased competition affect credit ratings?," NBER Working Papers 16404, National Bureau of Economic Research, Inc.
  2. Bruno Strulovici & Darrell Duffie, 2009. "Capital Mobility and Asset Pricing," 2009 Meeting Papers 87, Society for Economic Dynamics.


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