Date of Award

8-11-2005

Degree Type

Closed Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Risk Management and Insurance

First Advisor

Richard D Phillips - Chair

Second Advisor

Neil A Doherty

Third Advisor

Sanjay Srivastava

Fourth Advisor

Jayant R Kale

Fifth Advisor

Ajai Subramanian

Abstract

Despite the recognized importance of the bond rating industry, little academic work has been done to investigate the determinants of the standards these firms employ to assign credit ratings to individual firms. There is an ongoing debate in the literature arguing whether the decline in the percentage of highly rated firms is because rating standards have become more stringent over time or whether the credit quality of firms in the economy has declined. We investigate this question in this dissertation. Our first contribution is to address several empirical problems in prior literature. This study uses a combination of structural models of default and econometric model of ratings to study the determinants of rating standards and, by doing so, overcome the earlier methodological shortcomings. Our second contribution is to test new theory which hypothesizes that the standards of a rating agency are conditional upon the distribution of default risk in the economy at the time. The results are robust no matter which structural models of default we employ. The evidence suggests the standards are relative to the default risk distribution and there has been a secular increase in the stringency in the assignment of ratings over time. A third way we extend the literature is by examining the accuracy of the assignment of ratings. Theoretical models suggest rating agencies have incentives to purposefully add noise to the assignment of ratings. We conduct an empirical analysis of the classification errors using receiver operating characteristic analysis. The results suggest that error rates have decreased at the extreme ends of the rating spectrum (AAA vs. AA and below; B and below vs. BB and above) over time while it has increased in the middle rating categories. This error rate is directly related to the distribution of default risk across firms at any point in time. These findings not only strengthen our result that standards are relative and time varying, but also suggest there is more noise in the assignment of ratings at exactly the time when there is more uncertainty regarding the credit risk of firms in the economy – i.e., during a credit crisis.

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