Démocratie et justice sociale : Arrow-Harsanyi- Rawls-Sen, un quatuor dissonant

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Démocratie et justice sociale : Arrow-Harsanyi- Rawls-Sen, un quatuor dissonant

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Pre-play communication and credibility: A test of Aumann's conjecture

The effectiveness of pre-play communication in achieving efficientoutcomes has long been a subject of controversy. In some environments,cheap talk may help to achieve coordination. However, Aumannconjectures that, in a variant of the Stag Hunt game, a signal forefficient play is not self-enforcing and concludes that an "agreementto play [the efficient outcome] conveys no information about what theplayers will do." Harsanyi and Selten (1988) cite this example as anillustration of risk-dominance vs. payoff-dominance. Farrell and Rabin(1996) agree with the logic, but suspect that cheap talk willnonetheless achieve efficiency. The conjecture is tested with one-waycommunication. When the sender first chooses a signal and then anaction, there is impressive coordination: a 94% probability for thepotentially efficient (but risky) play, given a signal for efficientplay. Without communication, efforts to achieve efficiency wereunsuccessful, as the proportion of B moves is only 35%. I also test ahypothesis that the order of the action and the signal affects theresults, finding that the decision order is indeed important. WhileAumann s conjecture is behaviorally disconfirmed when the signal isdetermined initially, the signal s credibility seems to be much moresuspect when the sender is known to have first chosen an action, andthe results are not statistically distinguishable from those whenthere is no signal. Some applications and issues in communication andcoordination are discussed.

Endogenous price leadership

We consider a linear price setting duopoly game with di®erentiatedproducts and determine endogenously which of the players will lead andwhich will follow. While the follower role is most attractive for each firm, we show that waiting is more risky for the low cost firm so that,consequently, risk dominance considerations, as in Harsanyi and Selten(1988), allow the conclusion that only the high cost firm will choose towait. Hence, the low cost firm will emerge as the endogenous price leader.

Endogenous price leadership

We consider a linear price setting duopoly game with differentiated products and determine endogenously which of the players will lead and which will follow. While the follower role is most attractive for each firm, we show that waiting is more risky for the low cost firm so that, consequently, risk dominance considerations, as in Harsanyi and Selten (1988), allow the conclusion that only the highcost firm will choose to wait. Hence, the low cost firm will emerge as the endogenous price leader.

Endogenous Stackelberg leadership

We consider a linear quantity setting duopoly game and analyzewhich of the players will commit when both players have the possibility todo so. To that end, we study a 2-stage game in which each player caneither commit to a quantity in stage 1 or wait till stage 2. We show thatcommitting is more risky for the high cost firm and that, consequently,risk dominance considerations, as in Harsanyi and Selten (1988), allowthe conclusion that only the low cost firm will choose to commit.Hence, the low cost firm will emerge as the endogenous Stackelberg leader.

Risk dominance selects the leader. An experimental analysis

Coordination games arise very often in studies of industrial organization and international trade. This type of games has multiple strict equilibria, and therefore the identification of testable predictions isvery difficult. We study a vertical product differentiation model with two asymmetric players choosing first qualities and then prices. This game has two equilibria for some parameter values. However, we apply the risk dominance criterion suggested by Harsanyi and Selten and show that it always selects the equilibrium where the leader is the firm having some initial advantage. We then perform an experimental analysis totest whether the risk dominance prediction is supported by the behaviour oflaboratory agents. We show that the probability that the risk dominance prediction is right depends crucially on the degree of asymmetry of the game. The stronger the asymmetries the higher the predictive power of the risk dominance criterion.

Interpersonal comparison of welfare in Harsanyi’s veil-of-ignorance model

Selon le voile d’ignorance proposé par John Harsanyi (1953, 1955), l’observateur rationnel derrière le voile d’ignorance cherche à maximiser la somme des utilités individuelles. Cependant, le modèle d’Harsanyi est fondé sur une hypothèse erronée que la fonction d’utilité à la von Neumann-Morgenstern de l’observateur permet la comparaison interpersonnelle de bien-être. Ce papier suggère une modification du modèle d’Harsanyi qui permet la comparaison interpersonnelle de bien-être, en utilisant les années de vie en parfaite utilité ou les années de vie heureuse comme mesure du bien-être.

Non-Consequentialist Utilitarianism

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Théorie des jeux expérimentale & action motrice

How do sportspeople succeed in a non-collaborative game? An illustration of a perverse side effect of altruism Are team sports specialists predisposed to collaboration? The scientific literature on this topic is divided. The present article attempts to end this debate by applying experimental game theory. We constituted three groups of volunteers (all students aged around 20): 25 team sports specialists; 23 individual sports specialists (gymnasts, track & field athletes and swimmers) and a control group of 24 non-sportspeople. Each subgroup was divided into 3 teams that played against each other in turn (and not against teams from other subgroups). The teams played a game based on the well-known Prisoner's Dilemma (Tucker, 1950) - the paradoxical "Bluegill Sunbass Game" (Binmore, 1999) with three Nash equilibria (two suboptimal equilibria with a pure strategy and an optimal equilibrium with a mixed, egotistical strategy (p= 1/2)). This game also features a Harsanyi equilibrium (based on constant compliance with a moral code and altruism by empathy: "do not unto others that which you would not have them do unto you"). How, then, was the game played? Two teams of 8 competed on a handball court. Each team wore a distinctive jersey. The game lasted 15 minutes and the players were allowed to touch the handball ball with their feet or hands. After each goal, each team had to return to its own half of the court. Players were allowed to score in either goal and thus cooperate with their teammates or not, as they saw fit. A goal against the nominally opposing team (a "guardian" strategy, by analogy with the Bluegill Sunbass Game) earned a point for everyone in the team. For an own goal (a "sneaker" strategy), only the scorer earned a point - hence the paradox. If all the members of a team work together to score a goal, everyone is happy (the Harsanyi solution). However, the situation was not balanced in the Nashian sense: each player had a reason to be disloyal to his/her team at the merest opportunity. But if everyone adopts a "sneaker" strategy, the game becomes a free-for-all and the chances of scoring become much slimmer. In a context in which doubt reigns as to the honesty of team members and "legal betrayals", what type of sportsperson will score the most goals? By analogy with the Bluegill Sunbass Game, we recorded direct motor interactions (passes and shots) based on either a "guardian" tactic (i.e. collaboration within the team) or a "sneaker" tactic (shots and passes against the player's designated team). So, was the group of team sports specialist more collaborative than the other two groups? The answer was no. A statistical analysis (difference from chance in a logistic regression) enabled us to draw three conclusions: ?For the team sports specialists, the Nash equilibrium (1950) was stronger than the Harsanyi equilibrium (1977). ?The sporting principles of equilibrium and exclusivity are not appropriate in the Bluegill Sunbass Game and are quickly abandoned by the team sports specialists. The latter are opportunists who focus solely on winning and do well out of it. ?The most altruistic players are the main losers in the Bluegill Sunbass Game: they keep the game alive but contribute to their own defeat. In our experiment, the most altruistic players tended to be the females and the individual sports specialists

Théorie des jeux expérimentale & action motrice

How do sportspeople succeed in a non-collaborative game? An illustration of a perverse side effect of altruism Are team sports specialists predisposed to collaboration? The scientific literature on this topic is divided. The present article attempts to end this debate by applying experimental game theory. We constituted three groups of volunteers (all students aged around 20): 25 team sports specialists; 23 individual sports specialists (gymnasts, track & field athletes and swimmers) and a control group of 24 non-sportspeople. Each subgroup was divided into 3 teams that played against each other in turn (and not against teams from other subgroups). The teams played a game based on the well-known Prisoner's Dilemma (Tucker, 1950) - the paradoxical "Bluegill Sunbass Game" (Binmore, 1999) with three Nash equilibria (two suboptimal equilibria with a pure strategy and an optimal equilibrium with a mixed, egotistical strategy (p= 1/2)). This game also features a Harsanyi equilibrium (based on constant compliance with a moral code and altruism by empathy: "do not unto others that which you would not have them do unto you"). How, then, was the game played? Two teams of 8 competed on a handball court. Each team wore a distinctive jersey. The game lasted 15 minutes and the players were allowed to touch the handball ball with their feet or hands. After each goal, each team had to return to its own half of the court. Players were allowed to score in either goal and thus cooperate with their teammates or not, as they saw fit. A goal against the nominally opposing team (a "guardian" strategy, by analogy with the Bluegill Sunbass Game) earned a point for everyone in the team. For an own goal (a "sneaker" strategy), only the scorer earned a point - hence the paradox. If all the members of a team work together to score a goal, everyone is happy (the Harsanyi solution). However, the situation was not balanced in the Nashian sense: each player had a reason to be disloyal to his/her team at the merest opportunity. But if everyone adopts a "sneaker" strategy, the game becomes a free-for-all and the chances of scoring become much slimmer. In a context in which doubt reigns as to the honesty of team members and "legal betrayals", what type of sportsperson will score the most goals? By analogy with the Bluegill Sunbass Game, we recorded direct motor interactions (passes and shots) based on either a "guardian" tactic (i.e. collaboration within the team) or a "sneaker" tactic (shots and passes against the player's designated team). So, was the group of team sports specialist more collaborative than the other two groups? The answer was no. A statistical analysis (difference from chance in a logistic regression) enabled us to draw three conclusions: ?For the team sports specialists, the Nash equilibrium (1950) was stronger than the Harsanyi equilibrium (1977). ?The sporting principles of equilibrium and exclusivity are not appropriate in the Bluegill Sunbass Game and are quickly abandoned by the team sports specialists. The latter are opportunists who focus solely on winning and do well out of it. ?The most altruistic players are the main losers in the Bluegill Sunbass Game: they keep the game alive but contribute to their own defeat. In our experiment, the most altruistic players tended to be the females and the individual sports specialists

Théorie des jeux expérimentale & action motrice

How do sportspeople succeed in a non-collaborative game? An illustration of a perverse side effect of altruism Are team sports specialists predisposed to collaboration? The scientific literature on this topic is divided. The present article attempts to end this debate by applying experimental game theory. We constituted three groups of volunteers (all students aged around 20): 25 team sports specialists; 23 individual sports specialists (gymnasts, track & field athletes and swimmers) and a control group of 24 non-sportspeople. Each subgroup was divided into 3 teams that played against each other in turn (and not against teams from other subgroups). The teams played a game based on the well-known Prisoner's Dilemma (Tucker, 1950) - the paradoxical "Bluegill Sunbass Game" (Binmore, 1999) with three Nash equilibria (two suboptimal equilibria with a pure strategy and an optimal equilibrium with a mixed, egotistical strategy (p= 1/2)). This game also features a Harsanyi equilibrium (based on constant compliance with a moral code and altruism by empathy: "do not unto others that which you would not have them do unto you"). How, then, was the game played? Two teams of 8 competed on a handball court. Each team wore a distinctive jersey. The game lasted 15 minutes and the players were allowed to touch the handball ball with their feet or hands. After each goal, each team had to return to its own half of the court. Players were allowed to score in either goal and thus cooperate with their teammates or not, as they saw fit. A goal against the nominally opposing team (a "guardian" strategy, by analogy with the Bluegill Sunbass Game) earned a point for everyone in the team. For an own goal (a "sneaker" strategy), only the scorer earned a point - hence the paradox. If all the members of a team work together to score a goal, everyone is happy (the Harsanyi solution). However, the situation was not balanced in the Nashian sense: each player had a reason to be disloyal to his/her team at the merest opportunity. But if everyone adopts a "sneaker" strategy, the game becomes a free-for-all and the chances of scoring become much slimmer. In a context in which doubt reigns as to the honesty of team members and "legal betrayals", what type of sportsperson will score the most goals? By analogy with the Bluegill Sunbass Game, we recorded direct motor interactions (passes and shots) based on either a "guardian" tactic (i.e. collaboration within the team) or a "sneaker" tactic (shots and passes against the player's designated team). So, was the group of team sports specialist more collaborative than the other two groups? The answer was no. A statistical analysis (difference from chance in a logistic regression) enabled us to draw three conclusions: ?For the team sports specialists, the Nash equilibrium (1950) was stronger than the Harsanyi equilibrium (1977). ?The sporting principles of equilibrium and exclusivity are not appropriate in the Bluegill Sunbass Game and are quickly abandoned by the team sports specialists. The latter are opportunists who focus solely on winning and do well out of it. ?The most altruistic players are the main losers in the Bluegill Sunbass Game: they keep the game alive but contribute to their own defeat. In our experiment, the most altruistic players tended to be the females and the individual sports specialists

Type space on a purely measurable parameter space

Several game theoretical topics require the analysis of hierarchical beliefs, particularly in incomplete information situations. For the problem of incomplete information, Hars´anyi suggested the concept of the type space. Later Mertens & Zamir gave a construction of such a type space under topological assumptions imposed on the parameter space. The topological assumptions were weakened by Heifetz, and by Brandenburger & Dekel. In this paper we show that at very natural assumptions upon the structure of the beliefs, the universal type space does exist. We construct a universal type space, which employs purely a measurable parameter space structure.