The wide dispersion of credit spreads
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Ratings are designed to reflect credit risk over time. Two bonds from different issuers that share the major characteristics, for example with respect to the degree of structural and legal subordination, coupon and embedded optionality, and additionally have the same rating, should trade approximately at the same level. Bond spreads of course also depend on maturity, yielding a term structure of credit spreads. The average spread of an issuer within a particular rating class furthermore depends on the liquidity of the individual bonds and its sector classification.
Despite the wide dispersion of credit spreads within the rating buckets the general link between credit spreads and ratings is clear, with average spread increasing as credit quality decreases. However, as our study illustrates there are large overlaps between individual rating distributions. Myriad examples can be found to show that market participants often perceive the risk of one company in comparison to another to be completely different, even if both have the same rating. It should be noted that our sturdy includes bonds with rather different maturities and coupons.
Altman (1989) and Taylor and Perraudin (2001) have shown the presence of highly persistent inconsistencies between credit ratings and bond spreads, even after adjusting for liquidity and potential tax effects.