Coherent Risk Measures (page 188) !
Define a coherent risk measure as the amount of cash that has to be added to a portfolio to make its risk acceptable !
Properties of coherent risk measure !
If one portfolio always produces a worse outcome than another its risk measure should be greater !
If we add an amount of cash K to a portfolio its risk measure should go down by K !
Changing the size of a portfolio by λ should result in the risk measure being multiplied by λ
The risk measures for two portfolios after they have been merged should be no greater than the sum of their risk measures before they were merged