FRM Part II · FRM Exam Part II · Beyond Exceedance-Based Backtesting of Value-at-Risk Models
Two banks each report 99% one-day VaR of USD 10 million and each records exactly 3 exceptions in 250 days. Bank A's exception losses averaged USD 11 million; Bank B's averaged USD 40 million. Which conclusion is most consistent with the limitations of exceedance-based backtesting?
Identical exception counts make the two banks indistinguishable to count-based tests, yet Bank B's exceedances average USD 40 million versus 11 million for Bank A. The test is blind to severity, so Bank B's worse tail risk goes undetected.
- ABank B's model is better because its VaR was exceeded by larger amounts, showing higher sensitivity
- BThe banks' models are equivalent because exception counts are identical and the test cannot separate them, though Bank B's tail risk is clearly worse than the test indicatesCorrect
- CBank A's model should be rejected because its exceptions are smaller
- DOnly Bank B passes the Basel traffic-light test because its losses are larger
Explanation
Both have 3 exceptions, so any count-based test (Kupiec or traffic light) gives identical results. The severity differs greatly (11 vs 40 million), which exceedance tests ignore. Bank B's heavy tail is hidden, so magnitude-based approaches such as expected shortfall backtests or loss-function measures are needed.
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