FRM Part II · FRM Exam Part II · Beyond Exceedance-Based Backtesting of Value-at-Risk Models
A validator finds that a bank's VaR model passes the Kolmogorov-Smirnov test on its PIT values, but she suspects the model misstates extreme tail losses. Which test is better suited to this concern, and why?
Anderson-Darling is better suited, because it places extra weight on discrepancies in the tails of the distribution, whereas Kolmogorov-Smirnov looks at the maximum gap, which is usually driven by the center. Kupiec tests only the exceedance frequency at one level.
- AAnderson-Darling, because it weights discrepancies in the tails more heavily than KSCorrect
- BKolmogorov-Smirnov with a larger sample, because it is most sensitive in the tails
- CAnderson-Darling, because it only examines the central part of the distribution
- DKupiec proportion-of-failures test, because it tests the entire distribution shape
Explanation
KS measures the maximum gap, which is typically greatest near the center and is relatively insensitive to tail differences. Anderson-Darling applies a weighting that emphasizes the tails, making it more powerful against tail misspecification. Kupiec only tests the exceedance frequency at one confidence level.
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