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Theoretical assumptions of IRB in credit risk capital adequacy evaluation
Tomasz Zieliński
Abstract
A key area of concern for banking supervisors is solvency of banking institutions, which determines the stability of the entire banking sector. In the common opinion of regulators, equity capital is the best protection against unexpected losses. The main proponent of this approach has been for many years the Basel Committee on Banking Supervision. The evolution of the Basel agreements is aimed at improving the protection against increasing forms of risk, yet in the common opinion, credit risk still plays a dominant role. At the moment there are two main methods for estimating the capital requirement for credit risk, known as the Standard Approach
and the Internal Ratings Approach. The Standard Approach is simple, intuitive and consequently does not require detailed explanations. The Internal Rating Based Approach, on the other hand, is based on a complex mathematical formula, comprehensible only to a very small group of specialists. The purpose of this paper is to explain the basic assumptions of the IRB framework. This explanation has been simplified as much as possible. Detailed mathematical and statistical proofs are replaced with an intuitive explanation, referring to the typical experience of bankers.
The IRB formula framework is actually modified by the banking regulations and adapted to various types of credit exposures. The general assumptions, however, remain unchanged. Understanding the main objectives of the IRB formula opens up further discussion on its relevance to the measurement of actual exposure to credit risk.
Keywords:
bank, credit risk, capital adequacy, IRB, standardized approach, Internal Rating-Based ApproachDetails
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