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The ultimatum game is probably the most appraised, simple game with the fiercest debate in the experimental literature about the differences between actual behavior and game-theoretical logic. As a consequence, a large body of literature about behavioral models encompassing theory and behavioral findings has emerged. We discuss the original paper’s many ideas, highlighting its design features and results connected to today’s experimental standards. We conclude with a hit list of topics the ultimatum game has inspired in economics and multiple other disciplines.

Modern societies offer a large variety of choices1,2, which is generally thought to be valuable3-7. But having too much choice can be detrimental1-3,8-11 if the costs of choice outweigh its benefits due to 'choice overload'12-14. Current explanatory models of choice overload mainly derive from behavioural studies13,14. A neuroscientific investigation could further inform these models by revealing the covert mental processes during decision-making. We explored choice overload using functional magnetic resonance imaging while subjects were either choosing from varying-sized choice sets or were browsing them. When choosing from sets of 6, 12 or 24 items, functional magnetic resonance imaging activity in the striatum and anterior cingulate cortex resembled an inverted U-shaped function of choice set size. Activity was highest for 12-item sets, which were perceived as having 'the right amount' of options and was lower for 6-item and 24-item sets, which were perceived as 'too small' and 'too large', respectively. Enhancing choice set value by adding a dominant option led to an overall increase of activity. When subjects were browsing, the decision costs were diminished and the inverted U-shaped activity patterns vanished. Activity in the striatum and anterior cingulate reflects choice set value and can serve as neural indicator of choice overload.

Research summary Pursuing sources of entrepreneurial and competitive advantage, researchers have been exploring cognition. We examine how cognitive capabilities affect competitive performance, drawing on two constructs rooted in psychology and economics. A familiar one is analytic skill, the ability to solve abstract problems. To that, we add strategic intelligence — the ability to anticipate competitors’ behavior and preempt it. Using incentivized experiments, we measure the constructs in participants, then let them compete for cash in a highly competitive market. Although the market is designed to eliminate any advantages, whether from market structure or strategic resources, some profit much more than others. We trace performance differences to heterogeneity in analytic skill and strategic intelligence, and show how the two fuel superior performance, even against tough competition. (122 words) Managerial summary Why do some entrepreneurs outperform others? How can companies succeed against tough competition? Certainly, some benefit from unique resources, such as patents, and others can winnow competition, as through mergers. But some have entered highly competitive markets, lacking obvious resources, yet managed to achieve impressive success: think Under Armour, Wal-Mart or Home Depot. Here we test how advantage can stem from managerial cognition. First, we first measure two kinds of cognitive skill in market participants, and then we let them vie for cash in intensely competitive markets. Some end up with far more profit than others. Tracing the root of high performance, we find it is predicted by a combination of analytic skills, the ability to solve abstract problems, and strategic intelligence — ability to anticipate competitors’ behavior and preempt it. (130 words)

The great recession (2008) triggered an apparent discrepancy between empirical findings and macroeconomic models based on rational expectations alone. This gap led to a series of recent developments of a behavioral microfoundation of macroeconomics combined with the underlying experimental and behavioral Beauty Contest (BC) literature, which the authors review in this paper. They introduce the reader to variations of the Keynesian Beauty Contest (Keynes, The general theory of employment, interest, and money, 1936), theoretically and experimentally, demonstrating systematic patterns of out-of-equilibrium behavior. This divergence of (benchmark) solutions and bounded rationality observed in human behavior has been resolved through stepwise reasoning, the so-called level k, or cognitive hierarchy models. Furthermore, the authors show how the generalized BC function with limited parameter specifications encompasses relevant micro and macro models. Therefore, the stepwise reasoning models emerge naturally as building blocks for new behavioral macroeconomic theories to understand puzzles like the lacking rise of inflation after the financial crisis, the efficacy of quantitative easing, the forward guidance puzzle, and the effectiveness of temporary fiscal expansion. Nagel also acknowledges the grants PGC2018-098949-B-I00 from the Ministry of Education Madrid, and the travel grant Salvador de Madariaga 2019.

International audience; We study in a theoretical and experimental setting the interaction between belief-dependent preferences and reputation building in a finitely repeated trust game. We focus mainly on the effect of guilt aversion. In a simple two-type model, we analyze the effect of reputation building in the presence of guilt-averse trustees and derive behavioral predictions. We test these predictions in a laboratory experiment where we elicit information on trustees’ belief-dependent preferences and disclose it to the paired trustor before the repeated game.

We report the experimental results on a game with an outside option where forward induction contradicts with backward induction based on a focal, risk dominant equilibrium. The latter procedure yields the equilibrium selected by Harsanyi and Selten’s (1988) theory, which is hence here in contradiction with strategic stability (Kohlberg-Mertens (1985)). We …nd the Harsanyi-Selten solution to be in much better agreement with our data. Since fairness and bounded rationality seem to matter we discuss whether recent behavioral theories, in particular fairness theories and learning, might explain our …ndings. The fairness theories by Fehr and Schmidt (1999), Bolton and Ockenfels (2000) or Charness and Rabin (2002), when calibrated using experimental data on dictator- and ultimatum games, indeed predict that forward induction should play no role for our experiment and that the outside option should be chosen by all su¢ ciently sel…sh players. However, there is a multiplicity of “fairness equilibria”, some of which seem to be rejected because they require too many levels of reasoning. � We thank Prof. Reinhard Selten for his support in the design of the experiment and for many helpful discussions. The design of the basic game is due to him. We are grateful for the help received by those working at the Bonn Laboratory for Experimental Economics when preparing and conducting the experiment. We had several opportunities to present this work in seminars which resulted in many helpful comments and suggestions by the participants.

Uncertainty in the form of risk or ambiguity can arise from the interaction with nature and other players, while strategic uncertainty arises only in interactions with others. Here, we systematically compare binary decisions between a safe option and a potentially higher paying but uncertain option in four experimental conditions with the same potential monetary outcomes: coordination vs. anti coordination games, as well as risky and ambiguous lotteries. In each condition, we progressively increase the value of the safe option and measure subjects’ certainty equivalents (i.e., the specific safe payoff-threshold that makes a subject indifferent between the two options). We find that anti-coordination games and ambiguous lotteries elicit equally high aversion to uncertainty, relative to the other domains. In spite of this similarity, we find that subjects alternate between the safe and uncertain options much more frequently, thus displaying higher entropy, under anti-coordination relative to any of the other environments. These differences are predicted by theories of recursive reasoning in strategic games (e.g., thinking what others think we think etc.). Indeed, this can occur when interacting with intentional counterparts, but not with nature. This study was funded by the European Research Council, grant number 617629.

In social interactions, strategic uncertainty arises when the outcome of one’s choice depends on the choices of others. An important question is whether strategic uncertainty can be resolved by assessing subjective probabilities to the counterparts’ behavior, as if playing against nature, and thus transforming the strategic interaction into a risky (individual) situation. By means of functional magnetic resonance imaging with human participants we tested the hypothesis that choices under strategic uncertainty are supported by the neural circuits mediating choices under individual risk and deliberation in social settings (i.e. strategic thinking). Participants were confronted with risky lotteries and two types of coordination games requiring different degrees of strategic thinking of the kind ‘I think that you think that I think etc.’ We found that the brain network mediating risk during lotteries (anterior insula, dorsomedial prefrontal cortex and parietal cortex) is also engaged in the processing of strategic uncertainty in games. In social settings, activity in this network is modulated by the level of strategic thinking that is reflected in the activity of the dorsomedial and dorsolateral prefrontal cortex. These results suggest that strategic uncertainty is resolved by the interplay between the neural circuits mediating risk and higher order beliefs (i.e. beliefs about others’ beliefs). This work was supported by the European Research Council (ERC Consolidator Grant 617629 to G.C.); Human Frontier Science Program Organization (for life science and physics) to G.C., A.B. and R.N.; Dirección General de Investigación Cientifíca y Técnica (ECO2011-25295) (ECO2008-01768), Barcelona Graduate School of Economics and the Generalitat de Catalunya to R.N. A.B. was also supported by the Projet Exploratoire Premier Soutien (PEPS) Bio-Maths-Info (BMI) of the CNRS–INRIA–INSERM.

We introduce a generalization of the Beauty Contest (BC) game as a framework that incorporates different models from micro- and macroeconomics by formulating their reduced forms as special cases of the BC. Examples include public good games, ultimatum games, Bertrand, Cournot, some auctions, asset markets, New-Keynesian, and general equilibrium models with sentiments/animal spirits. This becomes feasible by considering BC specifications with a best response or optimal action as a function of other players' aggregated actions. For characterizing an integrated account of heterogeneity in economics, as observed in BC experiments, we employ a non-equilibrium model, the so-called “level-k” model, based on one (or more) reference point(s) and (limited) iterated best responses. Level-k and related models thus bridge the gap between non-strategic (e.g. irrational, intuitive or random) behavior and equilibrium choices. We also give a brief overview of interactive decision-making within experimental economics, and discuss elicitation methods, cognitive and population measures, to better understand heterogeneity in human reasoning in general, and in economic experiments in particular.

Newsvendors, such as newspaper companies, face the challenge that they need to decide how many units to produce before facing the demand by customers, and that their products are perishable. Experimental studies have documented that individuals do not find the optimal solution to that problem when they are asked to solve it under controlled conditions in the laboratory. This paper sheds light on the cognitive processes that explain individuals' inability to act optimally, using the data by Nagel and Vriend (1999). These authors implement the problem as a game, in which subjects need to make two decisions: the number of units they produce, and the amount of resources spent on advertisement. While the advertisement decisions converge to the Nash equilibrium, average production is inconsistent with the equilibrium even after many rounds of play. Our findings are interesting. First, advertisement decisions are well-described by a hill-climbing algorithm, linking the adjustment steps to the posterior uncertainty. Second, the bias in production is consistent with Bayesian learning, predicting slow adjustment. Third, the volatility patterns in production are well-described by Thompson Sampling, a Bayesian heuristic from the Operations Research literature.

Werner Güth's ultimatum game played a key role in the development of multiple research areas, several of which are highlighted.

This paper introduces a mixture model based on the beta distribution, without pre-established means and variances, to analyze a large set of Beauty-Contest data obtained from diverse groups of experiments (Bosch-Domenech et al. 2002). This model gives a better fit of the experimental data, and more precision to the hypothesis that a large proportion of individuals follow a common pattern of reasoning, described as Iterated Best Reply (degenerate), than mixture models based on the normal distribution. The analysis shows that the means of the distributions across the groups of experiments are pretty stable, while the proportions of choices at different levels of reasoning vary across groups.

We used functional MRI (fMRI) to investigate human mental processes in a competitive interactive setting—the “beauty contest” game. This game is well-suited for investigating whether and how a player's mental processing incorporates the thinking process of others in strategic reasoning. We apply a cognitive hierarchy model to classify subject's choices in the experimental game according to the degree of strategic reasoning so that we can identify the neural substrates of different levels of strategizing. According to this model, high-level reasoners expect the others to behave strategically, whereas low-level reasoners choose based on the expectation that others will choose randomly. The data show that high-level reasoning and a measure of strategic IQ (related to winning in the game) correlate with the neural activity in the medial prefrontal cortex, demonstrating its crucial role in successful mentalizing. This supports a cognitive hierarchy model of human brain and behavior.

We perform an experiment on a pure coordination game with uncertainty about the payoffs. Our game is closely related to models that have been used in many macroeconomic and financial applications to solve problems of equilibrium indeterminacy. In our experiment, each subject receives a noisy signal about the true payoffs. This game (inspired by the “global” games of Carlsson and van Damme, Econometrica, 61, 989–1018, 1993) has a unique strategy profile that survives the iterative deletion of strictly dominated strategies (thus a unique Nash equilibrium). The equilibrium outcome coincides, on average, with the risk-dominant equilibrium outcome of the underlying coordination game. In the baseline game, the behavior of the subjects converges to the theoretical prediction after enough experience has been gained. The data (and the comments) suggest that this behavior can be explained by learning. To test this hypothesis, we use a different game with incomplete information, related to a complete information game where learning and prior experiments suggest a different behavior. Indeed, in the second treatment, the behavior did not converge to equilibrium within 50 periods in some of the sessions.We also run both games under complete information. The results are sufficiently similar between complete and incomplete information to suggest that risk-dominance is also an important part of the explanation. Publicado

The theory of global games has shown that coordination games with multiple equilibria may have a unique equilibrium if certain parameters of the payoff function are private information instead of common knowledge. We report the results of an experiment designed to test the predictions of this theory. Comparing sessions with common and private information, we observe only small differences in behavior. For common information, subjects coordinate on threshold strategies that deviate from the global game solution towards the payoff-dominant equilibrium. For private information, thresholds are closer to the global game solution than for common information. Variations in the payoff function affect behavior as predicted by comparative statics of the global game solution. Predictability of coordination points is about the same for both information conditions.

Neuroeconomics is a new discipline that integrates economics, psychology and neuroscience. It combines economic and psychological theories with neuroscientific methodologies. The use of neuroimaging, single-cell recording and other methods from neuroscience has allowed the study of the neural correlates of basic economic and psychological concepts. Examples of research conducted with neuroeconomic methods have been studies on the neural basis of risk and uncertainty, choice over time (present versus future), bargaining, competition and altruism.

Pursuing sources of entrepreneurial and competitive advantage, researchers have been exploring cognition. We examine how cognitive capabilities affect competitive performance, drawing on two constr...

We examine the effect of unilateral and mutual partner selection in the context of prisoner's dilemmas experimentally. Subjects play simultaneously several finitely repeated two-person prisoner's dilemma games. We find that unilateral choice is the best system. It leads to low defection and fewer singles than with mutual choice. Furthermore, with the unilateral choice setup we are able to show that intending defectors are more likely to try to avoid a match than intending cooperators. We compare our results of multiple games with single game PD-experiments and find no difference in aggregate behavior. Hence the multiple game technique is robust and might therefore be an important tool in the future for testing the use of mixed strategies.

We consider an oligopolistic market game, in which the players are competing firms in the same market of a homogeneous consumption good. The consumer side is represented by a fixed demand function. The firms decide how much to produce of a perishable consumption good, and they decide upon a number of information signals to be sent into the population in order to attract customers. Due to the minimal information provided, the players do not have a well-specified model of their environment. Given a simple mode of adaptive behavior, which we showed in a previous paper explained the data relatively well, our main objective here is to analyze whether experienced players behave differently to inexperienced players. Copyright 1999 by Oxford University Press.

We explore bargaining, using ultimatum games, when one party, the proposer, possesses private information about the pie size and can either misrepresent this information through untruthful statements (explicit deception) or through information-revealing actions (implicit deception). Our study is the first such direct comparison between two ways in which people can deceive. We find that requiring informed parties to make an explicit statement yields greater deception than when information is communicated implicitly, particularly for larger stakes. However, allowing the explicit statement to be accompanied by a promise of truthfulness reverses this effect. In contrast with many previous studies, we generally observe very high frequencies of dishonesty.

In society, power is often transferred to another person or group. A previous work studied the evolution of cooperation among robot players through a coalition formation game with a non-cooperative procedure of acceptance of an agency of another player. Motivated by this previous work, we conduct a laboratory experiment on finitely repeated three-person coalition formation games. Human players with different strength according to the coalition payoffs can accept a transfer of power to another player, the agent, who then distributes the coalition payoffs. We find that the agencies method for coalition formation is quite successful in promoting efficiency. However, the agent faces a tension between short-term incentives of not equally distributing the coalition payoff and the long-term concern to keep cooperation going. In a given round, the strong player in our experiment often resolves this tension approximately in line with the Shapley value and the nucleolus. Yet aggregated over all rounds, the payoff differences between players are rather small, and the equal division of payoffs predicts about 80% of all groups best. One reason is that the voting procedure appears to induce a balance of power, independent of the individual player's strength: Selfish subjects tend to be voted out of their agency and are further disciplined by reciprocal behaviors.

We analyze a bargaining protocol recently proposed in the literature vis-a-vis unconstrained negotiation. This new mechanism extracts “gains from trade” inherent in the differing valuation of two parties towards various issues where conflict exists. We assess the role of incomplete vs. complete information in the efficiency achieved by this new mechanism and by unconstrained negotiation. We find that unconstrained negotiation does best under a situation of complete information where the valuations of both bargaining parties are common knowledge. Instead, the newly proposed mechanism does best in a situation with incomplete information. The sources of inefficiencies in each of the two cases arise from the different strategic use of the available information.

Alain Ledoux, who was one of over 6,000 chess players taking part in Bühren and Frank´s (2012) online Beauty Contest experiment, turned out to be the forgotten inventor of that game. We reconstruct the birth of the Beauty Contest. In section 1 of our note, its first two authors outline the history of the game that metamorphosed into the famous guessing game experiment which was first run in the lab by Rosemarie Nagel. In section 2, Rosemarie Nagel adds further remarks and thoughts about the development of the experimental Beauty Contest.

We perform an experiment which provides a laboratory replica of some important features of the welfare state. In the experiment, all individuals in a group decide whether to make a costly effort, which produces a random (independent) outcome for each one of them. The group members then vote on whether to redistribute the resulting and commonly known total sum of earnings equally amongst themselves. This game has two equilibria, if played once. In one of them, all players make effort and there is little redistribution. In the other one, there is no effort and nothing to redistribute. A solution to the repeated game allows for redistribution and high effort, sustained by the threat to revert to the worst of these equilibria. Our results show that redistribution with high effort is not sustainable. The main reason for the absence of redistribution is that rich agents do not act differently depending on whether the poor have worked hard or not. The equilibrium in which redistribution may be sustained by the threat of punishing the poor if they do not exert effort is not observed in the experiment. Thus, the explanation of the behavior of the subjects lies in Hobbes, not in Rousseau. We gratefully acknowledge the financial support from Spain’s Ministry of Science and Innovation under grants CONSOLIDER INGENIO 2010 CSD2006-0016 (all authors), ECO2009-10531 (Cabrales), ECO2008-01768 (Nagel) and the Comunidad de Madrid under grant Excelecon (Cabrales), the Generalitat de Catalunya and the CREA program (Nagel), and project SEJ2007-64340 of Spain’s Ministerio de Educación y Ciencia (Rodríguez Mora).

We run experiments on English Auctions where the bidders already own a part (toehold) of the good for sale. The theory predicts a very strong (“explosive”) effect of even small toeholds. While asymmetric toeholds do have an effect on bids and revenues in the lab, which gets stronger the larger the asymmetry, it is not nearly as strong as predicted. We explain this by analyzing the flatness of the payoff functions, which leads to large deviations from the equilibrium strategies being relatively costless. This is a general fundamental weakness of this type of explosive equilibria, which makes them fail when human players are involved. Our analysis shows that a levels of reasoning model explains the results better where this equilibrium fails. Moreover, we find that although big toeholds can be effective in a takeover battle, the cost to acquire them might be higher than the strategic benefit they bring.

This paper is about experiments on two versions of ultimatum games with incomplete information, called the offer game and the demand game. We apply the strategy method, that is, each subject had to design a complete strategy in advance instead of reacting spontaneously to a situation which occurs in the game. Game theory predicts very similar outcomes for the offer and the demand games. Our experiments, however, show significant differences in behavior between both games. Using the strategy method, allows us to explore the motivations leading to those differences. Since each subject played the same version of the game eight rounds against changing anonymous opponents we can also study subjects' learning behavior. We propose a theory of boundedly rational behavior, called the “anticipation philosophy”, which is well supported by the experimental data.

Bounded rational behaviour is commonly observed in experimental games and in real life situations. Neuroeconomics can help to understand the mental processing underlying bounded rationality and out-of-equilibrium behaviour. Here we report results from recent studies on the neural basis of limited steps of reasoning in a competitive setting —the beauty contest game. We use functional magnetic resonance imaging (fMRI) to study the neural correlates of human mental processes in strategic games. We apply a cognitive hierarchy model to classify subject’s choices in the experimental game according to the degree of strategic reasoning so that we can identify the neural substrates of different levels of strategizing. We found a correlation between levels of strategic reasoning and activity in a neural network related to mentalizing, i.e. the ability to think about other’s thoughts and mental states. Moreover, brain data showed how complex cognitive processes subserve the higher level of reasoning about others. We describe how a cognitive hierarchy model fits both behavioural and brain data.La racionalidad limitada es un fenómeno observado de manera frecuente tanto en juegos experimentales como en situaciones cotidianas. La Neuroeconomía puede mejorar la comprensión de los procesos mentales que caracterizan la racionalidad limitada; en paralelo nos puede ayudar a comprender comportamientos que violan el equilibrio. Nuestro trabajo presenta resultados recientes sobre la bases neuronales del razonamiento estratégico (y sus límite) en juegos competitivos —como el juego del “beauty contest”. Estudiamos las bases neuronales del comportamiento estratégico en juegos con interacción entre sujetos usando resonancia magnética funcional (fMRI). Las decisiones de los participantes se clasifican acorde al grado de razonamiento estratégico: el llamado modelo de Jerarquías Cognitivas. Los resultados muestran una correlación entre niveles de razonamiento y actividad neuronal relacionada con el “mentalizing”, es decir, con la habilidad para pensar y atribuir pensamientos y estados mentales a otros individuos. Más aun, la actividad cerebral nos muestra que los procesos cognitivos complejos aparecen en los niveles superiores de razonamiento estratégico. Finalmente, nuestro trabajo evidencia que el modelo de Jerarquías Cognitivas describen bien el comportamiento y la actividad cerebral.

This paper introduces a mixture model based on the beta distribution, without preestablished means and variances, to analyze a large set of Beauty-Contest data obtained from diverse groups of experiments (Bosch-Dom`enech et al. 2002). This model gives a better fit of the experimental data, and more precision to the hypothesis that a large proportion of individuals follow a common pattern of reasoning, described as iterated best reply (degenerate), than mixture models based on the normal distribution. The analysis shows that the means of the distributions across the groups of experiments are pretty stable, while the proportions of choices at different levels of reasoning vary across groups.

What could be the relationship between Reinhard Selten and the dinos’ story? An easy answer is that he was Nagel’s “Doktorvater” (PhD advisor) and the guessing game was one of the topics in her thesis. A more challenging connection is to Reinhard Selten’s constant fear to be trapped and blinded by the mathematical reasoning of game theory as a description of human behavior like the dinos seem to be trapped in YEP, WOO. Doesn’t the dinos’ story how to play the game sound appealing? Certainly it does for many game theorists. When they play it a large proportion chooses 0 while the winning number among them is between 10 and 15! Other theorists, on the other hand, found the game rather boring since not playing the theory didn’t seem a surprise and at the same time a clear structure of behavior was not at hand.

Publisher Summary This chapter presents data from a series of experiments with human subjects to test how individuals form expectations of others' expectations. The experiment has much in common with Keynes' insight regarding the behavior of investors in financial markets, and therefore the game is called ‘beauty contest’ game in honor of Keynes. This chapter introduces new asymmetric guessing games in which subjects of the same group may have different parameters p or intervals to choose from in order to separate leading decision rules. The main difference was the high number of frequencies at or near the equilibrium. The choices closest to the winning number were typically those which came from subjects who did their own pre-experiments with students, friends or even with a newsgroup experiment.

We run experiments on English Auctions where the bidders already own a part (toehold) of the good for sale. The theory predicts a very strong effect of even small toeholds, however we find the effects are not so strong in the lab. We explain this by analyzing the flatness of the payoff functions, which leads to relatively costless deviations from the equilibrium strategies. We find that a levels of reasoning model explains the results better than the Nash equilibrium. Moreover, we find that although big toeholds can be effective, the cost to acquire them might be higher than the strategic benefit they bring. Finally our results show that in general the seller’s revenues fall when the playing field is uneven.

Patients with stage-I (very mild and mild) Alzheimer's disease were asked to participate in a Dictator Game, a type of game in which a subject has to decide how to allocate a certain amount of money between himself and another person. The game enables the experimenter to examine the influence of social norms and social preferences on the decision-making process. When the results of treatments involving Alzheimer's disease patients were compared with those of identical treatments involving patients with mild cognitive impairment or healthy control subjects, with similar ages and social backgrounds, no statistically significant difference was found. This finding suggests that stage-I Alzheimer's disease patients may be as capable of making decisions involving social norms and preferences as other individuals of their age. Whatever brain structures are affected by the disease, they do not appear to influence, at this early stage, the neural basis for cooperation-enhancing social interactions.

Patients with stage-I (very mild and mild) Alzheimer’s disease were asked to participate in a Dictator Game, a type of game in which a subject has to decide how to allocate a certain amount of money between himself and another person. The game enables the experimenter to examine the influence of social norms and social preferences on the decision-making process. When the results of treatments involving Alzheimer’s disease patients were compared with those of identical treatments involving patients with mild cognitive impairment or healthy control subjects, with similar ages and social backgrounds, no statistically significant difference was found. This finding suggests that stage-I Alzheimer’s disease patients may be as capable of making decisions involving social norms and preferences as other individuals of their age. Whatever brain structures are affected by the disease, they do not appear to influence, at this early stage, the neural basis for cooperation-enhancing social interactions.

We perform an experiment on social insurance to provide a laboratory replica of some important features of the welfare state. In the experiment, all individuals in a group decide whether to make a costly effort, which produces a random (independent) outcome for each one of them. The group members then vote on whether to redistribute the resulting and commonly known total sum of earnings equally amongst themselves. This game has two equilibria, if played once. In one of them, all players make effort and there is little redistribution. In the other one, there is no effort and nothing to redistribute. A solution to the repeated game allows for redistribution and high effort, by the threat to revert to the worst of these equilibria. Our results show that redistribution with high effort is not sustainable. The main reason for the absence of redistribution is that rich agents do not act differently depending on whether the poor have worked hard or not. There is no social contract by which redistribution may be sustained by the threat of punishing the poor if they do not exert effort. Thus, the explanation of the behavior of the subjects lies in Hobbes, not in Rousseau.

This paper develops a finite mixture distribution analysis of Beauty-Contest data obtained from diverse groups of experiments. ML estimation using the EM approach provides estimates for the means and variances of the component distributions, which are common to all the groups, and estimates of the mixing proportions, which are specific to each group. This estimation is performed without imposing constraints on the parameters of the composing distributions. The statistical analysis indicates that many individuals follow a common pattern of reasoning described as iterated best reply (degenerate), and shows that the proportions of people thinking at different levels of depth vary across groups.

Speculative Attacks can be modeled as a coordination game with multiple equilibria if the state of the economy is common knowledge. With private information there is a unique equilibrium. This raises the question whether public information may be destabilizing by allowing for self-fulfilling beliefs. We present an experiment that imitates a speculative attacks model and compare sessions with public and private information. In both treatments subjects use so-called threshold strategies that lie in between the risk dominant and payoff dominant equilibrium of the underlying complete information game. Our evidence suggests that there are no destabilizing effects due to public information. In contrary, predictability of attacks is slightly higher with public than with private information, but prior probability of attacks is also higher with public information. We also test the predictive power of refinement theories to explain actual behavior and reactions to parameter changes.

A potential source of instability of many economic models is that agents have little incentive to stick with the equilibrium. We show experimentally that this may matter with price competition. The control variable is a price floor, which increases the cost of deviating from equilibrium. Theoretically the floor allows competitors to obtain higher profits, as low prices are excluded. However, behaviorally the opposite is observed; with a floor competitors receive lower joint profits. An error model (logit equilibrium) captures some but not all the important features of the data. We provide statistical support for a complementary explanation, which refers to how "threatening" an equilibrium is. We discuss the economic import of these findings, concerning matters like resale price maintenance and auction design.