Asset return correlation in Basel II: implications for credit risk management

The Basel Committee is currently reviewing the Accord on capital adequacy. It should provide new approaches that are more sensitive to risks. This paper focuses on the Internal Rating Based Advanced approach for retail exposures, which is compared to a one systematic factor model in order to highlight the underlying hypotheses of Basel II. The Basel framework assumes that the asset return correlation is solely determined by the probability of default (PD). However, the one-factor model highlights the influence of the volatility of PD on the asset return correlation, especially for low PDs. The assumption of the Basel framework implies first that there may be opportunities for regulatory arbitrage. Second, as the regulatory capital curve is concave in PD, it gives an incentive to decompose the portfolio into segments only for reducing the capital requirement. Finally, the inaccurate measure of asset return correlation might be misleading for credit risk management. The Basel framework is applied to a large portfolio of retail contracts (35,787 individual automotive lease contracts) provided from a major European financial institution. We show that the outcomes of Basel II are empirically relevant.