Market behavior when preferences are generated by second-order stochastic dominance.

We develop a theory of decision making and General Equilibrium for contingent markets when incomplete preferences are generated by second-order stochastic dominance (SSD). Demand, Pareto-optima and equilibria dominance are fully characterized. Demands and equilibrium allocations are non-increasing functions of the pricing density and Pareto-optimal allocations are comonotone. They generalize mean–variance demands and CAPM equilibrium allocations which are non-increasing affine functions of the pricing density. They are not observationally distinguishable from those of von-Neumann–Morgenstern decision makers with increasing strictly concave utilities nor from those of strict risk averse non-expected utility maximizers. We also show that expenditure functions associated to second-order stochastic dominance, provide microeconomic foundations for a class of law invariant risk-measures used in mathematical finance.Market; Behavior; Stochastic;

Intertemporal Equilibria with Knightian Uncertainty

We study a dynamic and infinite-dimensional model with Knightian uncertainty modeled by incomplete multiple prior preferences. In interior efficient allocations, agents share a common risk-adjusted prior and use the same subjective interest rate. Interior efficient allocations and equilibria coincide with those of economies with subjective expected utility and priors from the agents' multiple prior sets. We show that the set of equilibria with inertia contains the equilibria of the economy with variational preferences anchored at the initial endowments. A case study in an economy without aggregate uncertainty shows that risk is fully insured, while uncertainty can remain fully uninsured. Pessimistic agents with Gilboa-Schmeidler's max-min preferences would fully insure risk and uncertainty.Knightian Uncertainty, Ambiguity, Incomplete Preferences, General Equilibrium Theory, No Trade

Optimal Demand for Contingent Claims when Agents have law Invariant Utilities.

We consider a class of law invariant utilities which contains the Rank Dependent Expected Utility (RDU) and the cumulative prospect theory (CPT). We show that the computation of demand for a contingent claim when utilities are within that class, although not as simple as in the Expected Utility (EU) case, is still tractable. Specific attention is given to the RDU and to the CPT cases. Numerous examples are fully solved.Constrained Optimization; Quantiles; Demand; Law Invariant Utilities;

Existence and monotonicity of solutions to moral hazard problems.

This paper provides a method to prove existence of solutions to some moral hazard problems with infinite set of outcomes. The argument is based on the concept of nondecreasing rearrangement and on a supermodular version of Hardy–Littlewood’s inequality. The method also provides qualitative properties of solutions. Both the cases of wage contracts and of insurance contracts are studied.Supermodularity; Rearrangements; First-order approach; Moral hazard;

Optimal risk sharing with background risk.

This paper examines qualitative properties of efficient insurance contracts in the presence of background risk. In order to get results for all strictly risk-averse expected utility maximizers, the concept of “stochastic increasingness” is used. Different assumptions on the stochastic dependence between the insurable and uninsurable risk lead to different qualitative properties of the efficient contracts. The new results obtained under hypotheses of dependent risks are compared to classical results in the absence of background risk or to the case of independent risks. The theory is further generalized to nonexpected utility maximizers.Efficient contracts; Stochastically increasing; Incomplete markets; Insurance;

Pareto efficiency for the concave order and multivariate comonotonicity

In this paper, we focus on efficient risk-sharing rules for the concave dominance order. For a univariate risk, it follows from a comonotone dominance principle, due to Landsberger and Meilijson [25], that efficiency is characterized by a comonotonicity condition. The goal of this paper is to generalize the comonotone dominance principle as well as the equivalence between efficiency and comonotonicity to the multi-dimensional case. The multivariate setting is more involved (in particular because there is no immediate extension of the notion of comonotonicity) and we address it using techniques from convex duality and optimal transportation

Overlapping risk adjusted sets of priors and the existence of efficient allocations and equilibria with short-selling

The theory of existence of equilibrium with short-selling is reconsidered under risk and ambiguity modelled by risk averse variational preferences. A sufficient condition for existence of efficient allocations is that the relative interiors of the risk adjusted sets of expectations overlap. This condition is necessary if agents are not risk neutral at extreme levels of wealths either positive or negative. It is equivalent to the condition that there does not exist mutually compatible trades, with non negative expected value with respect to any risk adjusted prior, strictly positive for some agent and some prior. It is shown that the more uncertainty averse and the more risk averse the agents, the more likely are efficient allocations and equilibria to exist.Uncertainty;risk;common prior;equilibria with shortselling;Variational preferences

No-arbitrage, overlapping sets of priors and the existence of efficient allocations and equilibria in the presence of risk and ambiguity

The theory of existence of equilibrium with short-selling is reconsidered under risk and ambiguity modelled by risk averse variational preferences. A sufficient condition for existence of efficient allocations is that the relative interiors of the risk adjusted sets of expectations overlap. This condition is necessary if agents are not risk neutral at extreme levels of wealths either positive or negative. It is equivalent to the condition that there does not exist mutually compatible trades, with non negative expected value with respect to any risk adjusted prior, strictly positive for some agent and some prior. It is shown that the more uncertainty averse and the more risk averse, the more likely are efficient allocations and equilibria to exist.Uncertainty, risk, common prior, equilibria with short-selling, variational preferences.

Overlapping sets of priors and the existence of efficient allocations and equilibria for risk measures

The overlapping expectations and the collective absence of arbitrage conditions introduced in the economic literature to insure existence of Pareto optima and equilibria with short-selling when investors have a single belief about future returns, is reconsidered. Investors use measures of risk. The overlapping sets of priors and the Pareto equilibrium conditions introduced by Heath and Ku for coherent risk measures are respectively reinterpreted as a weak no-arbitrage and a weak collective absence of arbitrage conditions and shown to imply existence of Pareto optima and Arrow-Debreu equilibria.Overlapping sets of priors;collective absence of arbitrage;equilibria with short-selling;measures of risk

Overlapping sets of priors and the existence of efficient allocations and equilibria for risk measures

The overlapping expectations and the collective absence of arbitrage conditions introduced in the economic literature to insure existence of Pareto optima and equilibria when short-selling is allowed and investors hold a single belief about future returns, is reconsidered. Investors use measures of risk. The overlapping sets of priors and the Pareto equilibrium conditions introduced by Heath and Ku for coherent risk measures are reinterpreted as a weak no-arbitrage and a weak collective absence of arbitrage conditions and shown to imply existence of Pareto optima and Arrow Debreu equilibria.Overlapping sets of priors, collective absence of arbitrage, equilibria with short-selling, risk sharing, measures of risk.