FRM Part I · FRM Exam Part I · Measures of Financial Risk
Which property distinguishes ES from VaR when assessing whether a risk measure is coherent?
ES satisfies subadditivity for any loss distribution, so the ES of a combined portfolio never exceeds the sum of the separate ES values. This makes ES a coherent risk measure, whereas VaR can violate subadditivity and penalise diversification.
- AES satisfies subadditivity, so the ES of a combined portfolio is no greater than the sum of the individual ES valuesCorrect
- BES fails subadditivity for portfolios of independent assets
- CES satisfies subadditivity only when returns are normally distributed
- DES is coherent because it ignores losses beyond VaR
Explanation
ES is a coherent measure: it satisfies monotonicity, translation invariance, positive homogeneity and subadditivity for any distribution. VaR can violate subadditivity, particularly with non-elliptical or discrete loss distributions. ES being coherent depends on averaging tail losses, not ignoring them.
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