The value at risk (V@R) is a very important risk measure with significant applications in finance (risk management, pricing, hedging, portfolio theory, etc), insurance (premium principles, optimal reinsurance, etc), production, marketing (newsvendor problem), etc. It also plays a critical role in regulation about risk (Basel, Solvency, etc), it is very appreciated by practitioners due to its intuitive interpretation, and it is the unique popular risk measure remaining finite for heavy tailed risks with unbounded expectation. Besides, ambiguous frameworks are becoming more and more usual in applications of risk analysis. Lack of data or committed errors may provoke discrepancies between real probabilities and estimated ones. This paper combines both V@R and ambiguous settings, and a new representation theorem for V@R is given. Consequently, inspired by previous studies dealing with coherent risk measures and their representation, we will give new methods to compute and optimize V@R under ambiguity. This seems to be a relevant finding because the analytical properties of V@R are very weak if one compares with a coherent risk measure. Indeed, V@R is neither continuous nor convex, which makes it very complicated to deal with it in mathematical approaches. Nevertheless, the results of this paper will allow us to transform computation and optimization problems involving V@R into continuous and differentiable problems.
KEYWORDSambiguity, heavy tail, representation theorem, value at risk
INTRODUCTIONRisk measures beyond the standard deviation are becoming more and more important in many applications of risk analysis. Indeed, most of them can be interpreted in terms of potential capital losses, while the standard deviation does not satisfy this property in many situations. Besides, the standard deviation is not consistent with the second-order stochastic dominance and the standard utility functions in the presence of asymmetries, 1 and this drawback is overcome by other risk measures.Among many other examples, the coherent risk measures 2 and the expectation bounded risk measures 3 are very popular for practitioners and researchers since they have good analytical properties such as subadditivity, convexity, and continuity, making it feasible to deal with them in complex mathematical approaches. Important examples of such measures are the conditional value at risk (CV@R) and the weighted conditional value at risk. 3 With respect to the coherent and expectation bounded risk measures above, the value at risk (V@R) presents several shortcomings. Indeed, it is neither continuous nor convex, making it complex many analytical studies. Nevertheless, V@R 414