This excerpt taken from the PNC 10-Q filed May 11, 2009.
OTTINonagency Residential Mortgage-Backed Securities and Asset-Backed Securities Collateralized by First-Lien and Second-Lien Residential Mortgage Loans
During the first quarter of 2009, we recognized credit losses of $136 million on 39 non-agency residential mortgage-backed securities and four asset-backed securities (those collateralized by first- and second-lien residential mortgage loans). To measure credit losses we compile relevant collateral details and performance statistics on a security-by-security basis. The securities are then processed through a series of pre-established filters that include minimum thresholds for external credit ratings, the ratio of delinquencies to current credit enhancement, market price and whether the respective tranche incurs a loss using a third party loss model.
Securities not passing all of the filters are subjected to further analysis. We develop assumptions for prepayment speed, a delinquency default multiplier, and loss severity for securities grouped by security type, based on the underlying collateral characteristics, and vintage. We also consider actual recent collateral performance and security structuring (e.g., cross-subordination that may not be adequately addressed in the standard analysis, and the existence of third party guarantees). The resulting projections of future performance and cash flows of the underlying collateral are then allocated to each security. Based on the results of the cash flow analysis, we determined whether it is likely we will recover the amortized cost basis of our securities.