Agreeable Bets with Multiple Priors

This paper considers a two agent model of trade with multiple priors. First, we characterize the existence of an agreeable bet on some event in terms of the set of priors. It is then shown that the existence of an agreeable bet on some event is a strictly stronger condition than the existence of an agreeable trade, whereas the two conditions are equivalent in the standard Bayesian framework. Secondly, we show that the two conditions are equivalent when the set of priors is the core of a convex capacity.multiple priors, convex capacity, agreeing and disagreeing, Choquet integralm

Agreeing to Disagree with Multiple Priors

We present an extension of Aumann's Agreement Theorem to the case of multiple priors. If agents update all their priors, then, for the Agreement Theorem to hold, it is sufficient to assume that they have closed, connected and intersecting sets of priors. On the other hand, if agents select the priors to be updated according to the maximum likelihood criterion, then, under these same assumptions, agents may still agree to disagree. For the Agreement Theorem to hold, it is also necessary to assume that the maximum likelihood priors are commonly known and not disjoint. To show that these hypotheses are necessary, we give several examples in which agents agree to disagree.Agreeing to disagree, multiple priors, Aumann's Agreement Theorem

Trade with Heterogeneous Multiple Priors

This paper presents a general framework to understand the possibility of a purely speculative trade under asymmetric information, where the decision making rule of each trader conforms to the multiple priors model (Gibloa and Schmeidler, 1989): the agents are interested in the minimum of the conditional expected value of trade where the minimum is taken over the set of posteriors. In this framework, we derive a necessary and sufficient condition on the sets of posteriors, thus implicitly on the updating rules adopted by the agents, for non-existence of trade such that it is always common knowledge that every agent expects a positive gain.no trade; dynamic consistency; interim efficiency; rectangularity

Efficient Allocations under Ambiguity

Important implications of the expected utility hypothesis and risk aversion are that if agents have the same probability belief, then consumption plans in every efficient allocation of resources under uncertainty are comonotone with the aggregate endowment, and if their beliefs are concordant, then the consumption plans are measurable with respect to the aggregate endowment. We study these two properties of efficient allocations for models of preferences that exhibit ambiguity aversion using the concept of conditional beliefs, which we introduce in this paper. We provide characterizations of such conditional beliefs for the standard models of preferences used in applications.Economic

Agreeing to Disagree with Multiple Priors

We present an extension of Aumann’s Agreement Theorem to the case of multiple priors. If agents update all their priors, then, for the Agreement Theorem to hold, it is sufficient to assume that they have closed, connected and intersecting sets of priors. On the other hand, if agents select the priors to be updated according to the maximum likelihood criterion, then, under these same assumptions, agents may still agree to disagree. For the Agreement Theorem to hold, it is also necessary to assume that the maximum likelihood priors are commonly known and not disjoint. To show that these hypothesis are necessary, we give several examples in which agents agree to disagree

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.

When does ambiguity fade away?

the prior support is finite, long-run ambiguity is known to be a possible outcome only if the learning problem is misspecified (Marinacci and Massari, 2019). We show that if the prior support is naturally rich, long-run ambiguity cannot occur

Incomplete preferences and equilibrium in contingent markets

This paper shows that betting or speculative trading between agents with incomplete preferences is likely to occur if agents have access to convex choice sets. This contrasts sharply with endowment economy models where preference incompleteness often hinders betting, speculative trading or mutually beneficial insurance arrangements. Our results imply that decision‐makers with identical tastes and identical feasible sets will potentially gain from speculative trade for generic status quo allocations. We also develop a framework for endogenizing the status quo allocations of decision‐makers that are treated exogenously in the existing literature. Finally, we provide a tractable differential representation of status quo allocations, equilibria and conditions where speculative trade may or may not emerge