1. A method for predicting expected and unexpected loss outcomes for a portfolio of loans using a computer system coupled to a database, the loans issued by a lender to a plurality of borrowers, said method comprising the steps of: recording key account and risk attributes in the database for a historical portfolio of loans issued by the lender, the historical portfolio of loans includes loans issued to borrowers that have experienced a financial default with the lender and an associated economic loss; recording actual default and loss information in the database for each borrower included within the historical portfolio of loans; comparing the key account and risk attributes with the actual default and loss information over a predetermined period of time, the comparison is performed by the computer; selecting a sample of loans from the historical portfolio of loans to determine loss drivers based on the comparison of the key account and risk attributes with the actual default and loss information, the loss drivers include the key account and risk attributes predictive of a loss; building a regression tree based model representing relationships between the loss drivers, and expected and unexpected loss outcomes for the historical portfolio of loans, the regression tree based model is built using the computer system; and predicting the expected and unexpected loss outcomes for a second portfolio of loans using the regression tree based model and the loss drivers for the second portfolio of loans, the second portfolio of loans includes borrowers that have not experienced a default with the lender.