Expected shortfall
From Wikipedia, the free encyclopedia
Expected shortfall is a measure of financial portfolio risk. It requires a quantile-level q, and is defined to be the expected loss of portfolio value given that the loss is occurring at or below the q-quantile.
For example, if we believe our average loss on the worst 5% of the possible outcomes for our portfolio is EUR 1000, then we could say our expected shortfall is EUR 1000 for the 5% tail.
Mathematically:
E(x | x > μ) where μ is the threshold.