The harmonic sequence paradox reconsidered

According to the harmonic sequence paradox (Blavatskyy 2006), an expected utility decision maker's willingness to pay for a gamble whose expected payoffs evolve according to the harmonic series is finite if and only if his marginal utility of additional income becomes eventually zero. Since the assumption of zero marginal utility is implausible, expected utility theory (as well as cumulative prospect theory) does apparently do a bad job in describing this decision behaviour. The present note demonstrates that the harmonic sequence paradox only applies to time-patient but not to time-impatient (risk-neutral) expected utility decision makers.St. Petersburg Paradox, Expected Utility, Time-Preferences

A Note on the Equivalence of Rationalizability Concepts in Generalized Nice Games

Moulin (1984) describes the class of nice games for which the solution concept of point-rationalizability coincides with iterated elimination of strongly dominated strategies. As a consequence nice games have the desirable property that all rationalizability concepts determine the same strategic solution. However, nice games are characterized by rather strong assumptions. For example, only single-valued best responses are admitted and the individual strategy sets have to be convex and compact subsets of the real line R1. This note shows that equivalence of all rationalizability concepts can be extended to multi-valued best response correspondences. The surprising finding is that equivalence does not hold for individual strategy sets that are compact and convex subsets of Rn with n>1.

Rational Expectations and Ambiguity: A Comment on Abel

Abel (2002) proposes a resolution of the riskfree rate and the equity premium puzzles by considering pessimism and doubt. Pessimism is characterized by subjective probabilistic beliefs about asset returns that are stochastically dominated by the objective distribution of these returns. The subjective distribution is characterized by doubt if it is a mean- preserving spread of the objective distribution. This note offers a decision theoretic foundation of Abel's ad-hoc definitions of pessimism and doubt under the assumption that individuals exhibit ambiguity attitudes in the sense of Schmeidler (1989). In particular, we show that the behavior of a representative agent, who resolves her uncertainty with respect to the true distribution of asset returns in a pessimistic way, is the equivalent to pessimism in Abel's sense. Furthermore, a representative agent, who takes into account pessimistic as well as optimistic considerations, may result in the equivalent to doubt in Abel's sense.

Dominance-Solvable Lattice Games

This paper derives sufficient and necessary conditions for dominance-solvability of so-called lattice games whose strategy sets have a lattice structure while they simultaneously belong to some metric space. The argument combines and extends Moulin's (1984) approach for nice games and Milgrom and Roberts' (1990) approach for supermodular games. The analysis covers - but is not restricted to - the case of actions being strategic complements as well as the case of actions being strategic substitutes. Applications are given for n-firm Cournot oligopolies, auctions with bidders who are optimistic - respectively pessimistic - with respect to an imperfectly known allocation rule, and Two-player Bayesian models of bank runs.

Equivalence between best responses and undominated

For games with expected utility maximizing players whose strategy sets are finite, Pearce (1984) shows that a strategy is strictly dominated by some mixed strategy, if and only if, this strategy is not a best response to some belief about opponents' strategy choice. This note generalizes Pearce's (1984) equivalence result to games with expected utility maximizing players whose strategy sets are arbitrary compact sets.

Equivalence between best responses and undominated strategies: a generalization from finite to compact strategy sets.

For games with expected utility maximizing players whose strategy sets are finite, Pearce (1984) shows that a strategy is strictly dominated by some mixed strategy, if and only if, this strategy is not a best response to some belief about opponents' strategy choice. This note generalizes Pearce''s (1984) equivalence result to games with expected utility maximizing players whose strategy sets are arbitrary compact sets.

A Parsimonious Model of Subjective Life Expectancy

This paper develops a theoretical model for the formation of subjective beliefs on individual survival expectations. Data from the Health and Retirement Study (HRS) indicate that, on average, young respondents underestimate their true sur- vival probability whereas old respondents overestimate their survival probability. Such subjective beliefs violate the rational expectations paradigm and are also not in line with the predictions of the rational Bayesian learning paradigm. We therefore introduce a model of Bayesian learning which combines rational learn- ing with the possibility that the interpretation of new information is prone to psychological attitudes. We estimate the parameters of our theoretical model by pooling the HRS data. Despite a parsimonious parametrization we find that our model results in a remarkable fit to the average subjective beliefs expressed in the data.

Uniqueness Conditions for Point-Rationalizable

The unique point-rationalizable solution of a game is the unique Nash equilibrium. However, this solution has the additional advantage that it can be justified by the epistemic assumption that it is Common Knowledge of the players that only best responses are chosen. Thus, games with a unique point-rationalizable solution allow for a plausible explanation of equilibrium play in one-shot strategic situations, and it is therefore desireable to identify such games. In order to derive sufficient and necessary conditions for unique point-rationalizable solutions this paper adopts and generalizes the contraction-property approach of Moulin (1984) and of Bernheim (1984). Uniqueness results obtained in this paper are derived under fairly general assumptions such as games with arbitrary metrizable strategy sets and are especially useful for complete and bounded, for compact, as well as for finite strategy sets. As a mathematical side result existence of a unique fixed point is proved under conditions that generalize a fixed point theorem due to Edelstein (1962).

Half empty, half full and the possibility of agreeing to disagree

Aumann (1976) derives his famous we cannot agree to disagree result under the assumption of rational Bayesian learning. Motivated by psychological evidence against this assumption, we develop formal models of optimistically, resp. pessimistically, biased Bayesian learning within the framework of Choquet expected utility theory. As a key feature of our approach the posterior subjective beliefs do, in general, not converge to "true" probabilities. Moreover, the posteriors of different people can converge to different beliefs even if these people receive the same information. As our main contribution we show that people may well agree to disagree if their Bayesian learning is psychologically biased in our sense. Remarkably, this finding holds regardless of whether people with identical priors apply the same psychologically biased Bayesian learning rule or not. A simple example about the possibility of ex-post trading in a financial asset illustrates our formal findings. Finally, our analysis settles a discussion in the no-trade literature (cf. Dow, Madrigal, and Werlang 1990, Halevy 1998) in that it clarifies that ex-post trade between agents with common priors and identical learning rules is only possible under asymmetric information.Common Knowledge, No-Trade Results, Rational Bayesian Learning, Bounded Rationality, Choquet Expected Utility Theory, Bayesian Updating, Dynamic Inconsistency

Revisiting independence and stochastic dominance for compound lotteries

We establish mathematical equivalence between independence of irrelevant alternatives and monotonicity with respect to first order stochastic dominance. This formal equivalence result between the two principles is obtained under two key conditions. Firstly, for all , each principle is defined on the domain of compound lotteries with compoundness level . Secondly, the standard concept of reduction of compound lotteries applies.