Split credit ratings and the prediction of bank ratings in the Basel II environment

Abstract

This thesis investigates two aspects of credit risk measurement in the context of Basel 11: The International Convergence of Capital Measurement and Capital Standards. The first is the problem arising when two credit rating agencies disagree over the rating assigned to an issuer and a split rating arises. The second area is the determination of internal credit rating models for use under the Internal ratings-based approach. This thesis presents a variety of bank rating modes for individual and long term ratings across different agencies and regions.

Using an extensive database of credit rating agencies with a sample of over 52,000 split ratings covering a four year period from 1999 - 2004 the first study shows that there is a ranking of agencies from the most to least generous that is stable over time. In most cases, the differences between the mean ratings of the agencies are significantly different from each other at the 1% level. The greatest differences arise between the US and Japanese agencies. When the split ratings are compared in terms of Basel II risk weights the differences between the US and Japanese agencies are still highly significant and the conclusion is that supervisors should alter the mapping of the Japanese agencies to the risk assessments under the provisions of Annex 2 to Basel II.

Contrary to earlier research this study does not find that the highest level of split ratings arise for banks. The level of consensus between agencies appears to correspond to the average credit quality of the industry in question.

Bank credit ratings are modelled from financial ratios and variables using ordinal logistic regression. Sample sizes exceeded 1,100 banks for the largest agencies.

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