8. Validation of Internal Estimates
CA-5.8.110
Banks must have a robust system in place to validate the accuracy and consistency of rating systems, processes, and the estimation of all relevant risk components. A bank must demonstrate to CBB that the internal validation process enables it to assess the performance of internal rating and risk estimation systems consistently and meaningfully.
Apr 08CA-5.8.111
Banks must regularly compare realised default rates with estimated PDs for each grade and be able to demonstrate that the realised default rates are within the expected range for that grade. Banks using the advanced IRB approach must complete such analysis for their estimates of LGDs and EADs. Such comparisons must make use of historical data that are over as long a period as possible. The methods and data used in such comparisons by the bank must be clearly documented by the bank. This analysis and documentation must be updated at least annually.
Apr 08CA-5.8.112
Banks must also use other quantitative validation tools and comparisons with relevant external data sources. The analysis must be based on data that are appropriate to the portfolio, are updated regularly, and cover a relevant observation period. Banks' internal assessments of the performance of their own rating systems must be based on long data histories, covering a range of economic conditions, and ideally one or more complete business cycles.
Apr 08CA-5.8.113
Banks must demonstrate that quantitative testing methods and other validation methods do not vary systematically with the economic cycle. Changes in methods and data (both data sources and periods covered) must be clearly and thoroughly documented.
Apr 08CA-5.8.114
Banks must have well-articulated internal standards for situations where deviations in realised PDs, LGDs and EADs from expectations become significant enough to call the validity of the estimates into question. These standards must take account of business cycles and similar systematic variability in default experiences. Where realised values continue to be higher than expected values, banks must revise estimates upward to reflect their default and loss experience.
Apr 08CA-5.8.115
Where banks rely on the CBB's, rather than internal estimates of risk parameters, they are encouraged to compare realised LGDs and EADs to those set by the CBB. The information on realised LGDs and EADs should form part of the bank's assessment of economic capital.
Apr 08
