Tribute to Jean-Yves Jaffray by the French Group of Decision Theory.

We argue, in the spirit of some of Jean-Yves Jaffray’s work, that explicitly incorporating the information, however imprecise, available to the decision maker is relevant, feasible, and fruitful. In particular, we show that it can lead us to know whether the decision maker has wrong beliefs and whether it matters or not, that it makes it possible to better model and analyze how the decision maker takes into account new information, even when this information is not an event and finally (...) that it is crucial when attempting to identify and measure the decision maker’s attitude toward imprecise information. (shrink)

Using a large sample of retail investors as well as experimental data we find that risk and ambiguity aversion are positively correlated. We provide evidence that a common link is decision mode: intuitive thinkers tolerate more risk and ambiguity than effortful reasoners. One interpretation is that intuitive thinking confers an advantage in risky or ambiguous situations. We present supporting lab and field evidence that intuitive thinkers outperform others in uncertain environments. Finally, we find that risk and ambiguity aversion vary with (...) individual characteristics and wealth. The wealthy are less risk averse but more ambiguity averse, which has implications for financial puzzles. (shrink)

Most decision-making research in economics focuses on individual decisions. Yet, we know, from psychological research in particular, that individual preferences can be sensitive to social pressures. In this paper, we study the impact of a group environment on individual preferences for risky and ambiguous prospects. In our experiment, each participant was invited to make a series of lottery-choice decisions in two different conditions. In the Alone condition, individuals made private choices, whereas in the Group condition, individuals belonged to a three-person (...) group and group members’ choices were aggregated according to either a majority or unanimity rule. This design allows us to study the impact of a group environment on individuals’ attitude towards both risky and ambiguous prospects, while controlling for the decision rule used in the group. Our experimental results show that when individuals are in the Group condition, they tend to be less risk averse and more ambiguity averse than when they are not part of a group. Our experiment also suggests that the decision rule matters as it shows that these two trends tend to be stronger when the group implements a unanimity rule. Specifically, we found that individuals who belong to a group implementing a unanimity rule are significantly less risk averse than individuals who belong to a group that relies on the majority rule. We obtained a similar—but non-significant—result under ambiguity. (shrink)

Coherent-ambiguity aversion is defined within the smooth-ambiguity model as the combination of choice-ambiguity and value-ambiguity aversion. Five ambiguous decision tasks are analyzed theoretically, where an individual faces two-stage lotteries with binomial, uniform, or unknown second-order probabilities. Theoretical predictions are then tested through a 10-task experiment. In tasks 1–5, risk aversion is elicited through both a portfolio choice method and a BDM mechanism. In tasks 6–10, choice-ambiguity aversion is elicited through the portfolio choice method, while value-ambiguity aversion comes about through the (...) BDM mechanism. The behavior of over 75 % of classified subjects is in line with the KMM model in all tasks 6–10, independent of their degree of risk aversion. Furthermore, the percentage of coherent-ambiguity-averse subjects is lower in the binomial than in the uniform and in the unknown treatments, with only the latter difference being significant. The most part of coherent-ambiguity-loving subjects show a high risk aversion. (shrink)

The objective of this study is to design a laboratory experiment to explore the effect of ambiguity on a subject’s search behavior in a finite-horizon sequential search model. In so doing, we employ a strategy to observe the potential trend of reservation points that is usually unobserved. We observe that subjects behaving consistently across treatments reduce their reservation points in the face of ambiguity over point distribution. Our result is consistent with the theoretical implication obtained by Nishimura and Ozaki.

We investigate risk and ambiguity attitudes among Ethiopian farmers in one of the poorest regions of the world. Strong risk aversion and ambiguity aversion were found with the Ethiopian farmers. We compared their attitudes to those of a Western university student sample elicited by the same decision task. Ambiguity aversion was similar for farmers and students, but farmers were more risk averse. Our results show that ambiguity aversion is not restricted to Western student populations, and that studies of agricultural decisions (...) may benefit from explicitly considering ambiguity attitudes. (shrink)

Les comportements individuels et collectifs en présence d’incertitude peuvent paraître irrationnels ou se modifier au cours du temps à la suite de nouvelles informations ou d’événements plus ou moins en lien avec ces incertitudes. Ceci pose la question des moyens mis à disposition des autorités publiques pour prévenir et gérer ces situations. Dans cet article, nous nous intéressons aux comportements des individus face aux situations incertaines en mettant en avant la manière dont la population peut percevoir ces incertitudes et les (...) informations provenant de sources diverses. Nous reprenons la littérature économique des comportements et prises de décision dans un environnement incertain afin de mettre en évidence les difficultés de la mise en place de politiques notamment d’incitation à la prévention. (shrink)