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Expected shortfall is a risk measure sensitive to the shape of the tail of the distribution of returns on a portfolio, unlike the more commonly used value-at-risk (VAR). Expected shortfall is calculated by averaging all of the returns in the distribution that are worse than the VAR of the portfolio at a given level of confidence. For instance, for a 95% confidence level, the expected shortfall is calculated by taking the average of returns in the worst 5% of cases.
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