A Theory of Rational Choice under Ignorance

This paper contributes to a theory of rational choice for decision-makers with incomplete preferences due to partial ignorance, whose beliefs are representable as sets of acceptable priors. We focus on the limiting case of `Complete Ignorance' which can be viewed as reduced form of the general case of partial ignorance. Rationality is conceptualized in terms of a `Principle of Preference-Basedness', according to which rational choice should be isomorphic to asserted preference. The main result characterizes axiomatically a new choice-rule called `Simultaneous Expected Utility Maximization'. It can be interpreted as agreement in a bargaining game (Kalai-Smorodinsky solution) whose players correspond to the (extremal) `acceptable priors' among which the decision maker has suspended judgment. An essential but non-standard feature of Simultaneous Expected Utility choices is their dependence on the entire choice set. This is justified by the conception of optimality as compromise rather than as superiority in pairwise comparisons.     

Conditional expected utility

Let \({\mathcal {E}}\) be a class of events. Conditionally Expected Utility decision makers are decision makers whose conditional preferences \(\succsim _{E}\), \(E\in {\mathcal {E}}\), satisfy the axioms of Subjective Expected Utility (SEU) theory. We extend the notion of unconditional preference that is conditionally EU to unconditional preferences that are not necessarily SEU. We study a subclass of these preferences, namely those that satisfy dynamic consistency. We give a representation theorem, and show that these preferences are Invariant Bi-separable in the sense of Ghirardato et al. (Journal of Economic Theory 118:133–173, 2004). We also show that these preferences have only a trivial overlap with the class of Choquet Expected Utility preferences, but there are plenty of preferences of the \(\alpha \)-Maxmin Expected Utility type that satisfy our assumptions. We identify several concrete settings where our results could be applied. Finally, we consider the special case where the unconditional preference is itself SEU, and compare our results with those of Fishburn (Econometrica 41:1–25, 1973).     

Are Groups More (or Less) Consistent Than Individuals?

There is now overwhelming experimental evidence that individuals systematically violate the axioms of Expected Utility theory. In reality, however, many economic decisions are taken by, or on behalf of, groups whose members have a joint stake in those decisions. This paper reports on an experiment in which pairs of individuals are tested for Common-Ratio inconsistencies. We find that the agreed choices of subject-pairs follow a pattern of inconsistency very close to that of individuals' choices. We also look for evidence that group participation increases the consistency of the individuals themselves. With one solitary exception, we find none.     

The bipolar Choquet integral representation

Cumulative Prospect Theory is the modern version of Prospect Theory and it is nowadays considered a valid alternative to the classical Expected Utility Theory. Cumulative Prospect theory implies Gain-Loss Separability, i.e., the separate evaluation of losses and gains within a mixed gamble. Recently, some authors have questioned this assumption of the theory, proposing new paradoxes where the Gain-Loss Separability is violated. We present a generalization of Cumulative Prospect Theory which does not imply Gain-Loss Separability and is able to explain the cited paradoxes. On the other hand, the new model, which we call the bipolar Cumulative Prospect Theory, genuinely generalizes the original Prospect Theory of Kahneman and Tversky, preserving the main features of the theory. We present also a characterization of the bipolar Choquet Integral with respect to a bi-capacity in a discrete setting.     

Elicitation of preferences under ambiguity

This paper is about behaviour under ambiguity—that is, a situation in which probabilities either do not exist or are not known. Our objective is to find the most empirically valid of the increasingly large number of theories attempting to explain such behaviour. We use experimentally-generated data to compare and contrast the theories. The incentivised experimental task we employed was that of allocation: in a series of problems we gave the subjects an amount of money and asked them to allocate the money over three accounts, the payoffs to them being contingent on a ‘state of the world’ with the occurrence of the states being ambiguous. We reproduced ambiguity in the laboratory using a Bingo Blower. We fitted the most popular and apparently empirically valid preference functionals [Subjective Expected Utility (SEU), MaxMin Expected Utility (MEU) and α-MEU], as well as Mean-Variance (MV) and a heuristic rule, Safety First (SF). We found that SEU fits better than MV and SF and only slightly worse than MEU and α-MEU.     

An axiomatization of cumulative prospect theory

This paper presents a method for axiomatizing a variety of models for decision making under uncertainty, including Expected Utility and Cumulative Prospect Theory. This method identifies, for each model, the situations that permit consistent inferences about the ordering of value differences. Examples of rankdependent and sign-dependent preference patterns are used to motivate the models and the “tradeoff consistency” axioms that characterize them. The major properties of the value function in Cumulative Prospect Theory—diminishing sensitivity and loss aversion—are contrasted with the principle of diminishing marginal utility that is commonly assumed in Expected Utility.     

Regret theory with general choice sets

The regret theory of choice under uncertainty proposed by Loomes and Sugden has performed well in explaining and predicting violations of Expected Utility theory. The original version of the model was confined to pairwise choices, which limited its usefulness as an economic theory of choice. Axioms for a more general form of regret theory have been proposed by Loomes and Sugden. In this article, it is shown that a simple nonmanipulability requirement is sufficient to characterize the functional form for regret theory with general choice sets. The stochastic dominance and comparative static properties of the model are outlined. A number of special cases are derived in which regret theory is equivalent to other well-known theories of choice under uncertainty.I would like to thank Graham Loomes, Robert Sugden, Peter Wakker, and Nancy Wallace for helpful comments and criticism.     

A comment on the axiomatics of the Maxmin Expected Utility model

Theory and Decision - Maxmin Expected Utility was first axiomatized by Gilboa and Schmeidler (1989) in an Anscombe–Aumann setup Anscombe and Aumann (1963) which includes exogenous...     

Time and risk

Intertemporal choice has obvious similarities with choice under uncertainty. However, because of technical difficulties in mapping results between the two domains, theoretical analysis of these topics has proceeded independently. In this article, we show that, using Rank Dependent Expected Utility rather than Expected Utility as the basic uncertain choice model, numerous analogies between the two fields may be identified and exploited. The key result is the derivation of a natural analogy between risk-aversion and impatience. This permits the reinterpretation of well-known results on stochastic dominance and comparative risk-aversion in the context of intertemporal choice. It is also possible to reinterpret results on intertemporal optimization in order to derive new results for portfolio choice problems under uncertainty.     

States of nature and states of mind: a generalized theory of decision-making

Canonical economic agents act so as to maximize a single, representative, utility function. However, there is accumulating evidence that heterogeneity in thought processes may be an important determinant of individual behavior. This paper investigates the implications of a vector-valued generalization of the Expected Utility paradigm, which permits agents either to deliberate as per Homo economics, or to act impulsively. This generalized decision theory is applied to explain the crowding-out effect, irrational educational investment decisions, persistent social inequalities, the pervasive influence of non-cognitive ability on socio-economic outcomes, and the dynamic relationships between non-cognitive ability, cognitive ability, and behavioral biases. These results suggest that the generalized decision theory warrants further investigation.

     

Assessing multiple prior models of behaviour under ambiguity

The recent spate of theoretical models of behaviour under ambiguity can be partitioned into two sets: those involving multiple priors and those not involving multiple priors. This paper provides an experimental investigation into the first set. Using an appropriate experimental interface we examine the fitted and predictive power of the various theories. We first estimate subject-by-subject, and then estimate and predict using a mixture model over the contending theories. The individual estimates suggest that 24% of our 149 subjects have behaviour consistent with Expected Utility, 56% with the Smooth Model, 11% with Rank Dependent Expected Utility and 9% with the Alpha Model; these figures are close to the mixing proportions obtained from the mixture estimates where the respective posterior probabilities of each of them being of the various types are 25%, 50%, 20% and 5%; and using the predictions 22%, 53%, 22% and 3%. The Smooth model appears the best.     

Noise and bias in eliciting preferences

In the context of eliciting preferences for decision making under risk, we analyse the features of four different elicitation methods—pairwise choice, willingness-to-pay, willingness-to-accept, and the Becker-DeGroot-Marschak mechanism—and estimate noise, bias and risk attitudes for two different preference functionals, Expected Utility and Rank-Dependent Expected Utility. It is well-known that methods differ in terms of the bias in the elicitation; it is rather less well-known that methods differ in terms of their noisiness. It has also been reported that risk attitudes are not stable across different elicitation methods. Our results suggest that elicited preferences should only be used in the context in which they were elicited, and the bias in the certainty-equivalent methods should be kept in mind when making predictions based on the elicited preferences. Moreover, conclusions should be moderated to take into account the various methods’ noise, which is generally lowest in the case of pairwise choice.     

Natural and artificial computing and reasoning in economic affairs

During a century or so, good reasoning in economic affairs was reduced to the search of computable algorithms for Expected Utility Optimization: but is the “Principle of least Action”, which was so powerful for guiding the researches in Physics and Natural Sciences as relevant as expected for guiding the good use of “reason in human affairs”? The discussion of the theoretical and practical weaknesses of the Paradigm of Expected Utility Optimization proposed since forty years notably by H. A. Simon, leads to the formulation of another paradigm, probably more relevant for the guidance of researches in economics and management affairs: “the Principle of Intelligent Action”, focus on the property of symbols computation systems. The general framework of Plausible Rationality, as established by G. Polya permits the formulation of programmable heuristics (or production rules) which can be expressed in terms of artificial symbolic computations. A more General Research Program is now open to research in Economic Reasoning by the developments of Artificial Intelligence and Cognitive Sciences: the design of relevant economic heuristics guiding the Decision Making Processes.     

Boundedly rational expected utility theory

We build a satisficing model of choice under risk which embeds Expected Utility Theory (EUT) into a boundedly rational deliberation process. The decision maker accumulates evidence for and against alternative options by repeatedly sampling from her underlying set of EU preferences until the evidence favouring one option satisfies her desired level of confidence. Despite its EUT core, the model produces patterns of behaviour that violate standard EUT axioms, while at the same time capturing systematic relationships between choice probabilities, response times and confidence judgments, which are beyond the scope of theories that do not take deliberation into account.

     

When is ambiguity–attitude constant?

This paper studies how updating affects ambiguity attitude. In particular we focus on generalized Bayesian updating of the Jaffray–Philippe sub-class of Choquet Expected Utility preferences. We find conditions for ambiguity attitude to be the same before and after updating. A necessary and sufficient condition for ambiguity attitude to be unchanged when updated on an arbitrary event is for the capacity to be neo-additive. We find a condition for updating on a given partition to preserve ambiguity attitude. We relate this to necessary and sufficient conditions for dynamic consistency. Finally, we study whether ambiguity increases or decreases after updating.     

Risk and time preferences of entrepreneurs: evidence from a Danish field experiment

To understand how small business entrepreneurs respond to government policy one has to know their risk and time preferences. Are they risk averse, or have high discount rates, such that they are hard to motivate? We have conducted a set of field experiments in Denmark that will allow a direct characterization of small business entrepreneurs in terms of these traits. We build on experimental tasks that are well established in the literature. The results do not suggest that small business entrepreneurs are more or less risk averse than the general population under the assumption of Expected Utility Theory. However, we generally find an S-shaped probability weighting function for both small business entrepreneurs and non-entrepreneurs, with entrepreneurs being more optimistic about the chance of occurrence for the best outcome in lotteries with real monetary outcomes. The results also point to a significant difference in individual discount rates between entrepreneurs and non-entrepreneurs: entrepreneurs are willing to wait longer for certain rewards than the general population.     

Uncertainty aversion and aversion to increasing uncertainty

According to the original Ellsberg (1961) examples there is uncertainty version if the decision maker prefers to bet on an urn of known composition rather than on an urn of unknown composition. According to another definition (Schmeidler, 1989), there is uncertainty aversion if any convex combination of two acts is preferred to the least favorable of these acts. We show that these two definitions differ: while the first one truly refers to uncertainty aversion, the second one refers to aversion to increasing uncertainty. Besides, with reference to Choquet Expected Utility theory, uncertainty aversion means that there exists the core of a capacity, while aversion to increasing uncertainty means that the capacity is convex. Consequently, aversion to increasing uncertainty implies uncertainty aversion, but the opposite does not hold. We also show that a completely analogous situation holds for the case of risk and we define a set of risk and uncertainty premiums according to the previous analysis.     

Emotional decision-makers and anomalous attitudes towards information

We use a simple version of the Psychological Expected Utility Model (Caplin and Leahy, Q J Econ 116:55–80, 2001) to analyze the optimal choice of information accuracy by an individual who is concerned with anticipatory feeling. The individual faces the following trade-off: on the one hand information may lead to emotional costs, on the other the higher the information accuracy, the higher the efficiency of decision-making. We completely and explicitly characterize how anticipatory utility depends on information accuracy, and study the optimal amount of information acquisition. We obtain simple and explicit conditions under which the individual prefers no-information or partial information gathering. We show that anomalous attitudes towards information can be more frequent and articulated than previously thought.     

Do Trade Union Leaders Violate Subjective Expected Utility? Some Insights From Experimental Data

This paper presents the results of two experiments designed to test violations of Subjective Expected Utility Theory (SEUT) within a sample of Italian trade union delegates and leaders. Subjects priced risky and ambiguous prospects in the domain of gains. Risky prospects were based on games of chance, while ambiguous prospects were built on the standard Ellsberg paradox and on event lotteries whose outcomes were based either on the results of a fictional election or on the future results of the 1999 European Parliamentary election in Italy and the U.K. The experiments show that, although risky prospects were priced at their expected values on average, trade union delegates and leaders did violate SEUT when assessing ambiguous prospects. Moreover, their behaviour depended on the source of uncertainty (Ellsberg paradox vs. electoral results; fictional vs. real election; Italy vs. U.K. election outcomes). We discuss the implications of these results for the economic theory of the trade union.