FRM Part I · FRM Exam Part I · Calculating and Applying VaR
A risk manager reviews four properties that a risk measure may satisfy: monotonicity, translation invariance, positive homogeneity and subadditivity. Value at Risk (VaR) is known to fail to be a coherent risk measure in general. Which property does VaR fail to satisfy in general?
VaR fails subadditivity in general. The VaR of a combined portfolio can exceed the sum of stand-alone VaRs, so diversification may appear to increase risk. VaR does satisfy monotonicity, translation invariance and positive homogeneity, which is why it is not coherent while expected shortfall is.
- AMonotonicity
- BTranslation invariance
- CSubadditivityCorrect
- DPositive homogeneity
Explanation
VaR satisfies monotonicity, translation invariance and positive homogeneity. It can violate subadditivity, so the VaR of a combined portfolio can exceed the sum of the individual VaRs, which is why VaR is not coherent. Expected shortfall satisfies all four properties.
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