Strategic Manipulation in Voting Games When Lotteries and Ties Are Permitted

A Gibbard-Satterthwaite type theorem is established for random decision rules and rules that permit ties. The rules use full information on how individuals rank lotteries and sets of outcomes. The theorem allows restrictions on the domain of rankings. Journal of Economic Literature Classification Numbers: D7, C7.     

Mindreading and Manipulation in an Ecology of Prisoner’s Dilemma Games: Laboratory Experiments

Synopsis Humans have a rational reason to seek out and selectively play Prisoner’s Dilemma games with others who (for whatever reason) will play cooperatively, while avoiding those who will defect. It follows that they also have reason to try and persuade others that they will personally cooperate if a game is joined (using the term from Evolutionary Psychology, to ‘manipulate’ others’ beliefs) and, thus, to penetrate to the truth underlying such efforts (to ‘mindread’ others intentions). We develop an economic model of mindreading and manipulation that can govern exchange relationships in natural circumstances, and report laboratory data showing that, absent constraining institutions that make play with cooperators likely, intending defectors are more likely to be chosen as partners than are intending cooperators. Intending defectors’ efforts at manipulation appear to be more successful than their potential victims’ efforts at mindreading. The findings suggest the nature of the problem that must be addressed for would-be traders in the absence of well-enforced rules governing contracts, and we discuss the patterns of behavior that are likely responses in such circumstances.     

The Promises and Problems of Games and Simulation

Many educators see the wave of the future in computer games and simulation. Lumsden gives an appreciation of the kind of games and simulations available and illustrates with specific detail how powerfully instructive some of these can be. He also makes a plea for scientific evaluation.     

Marriage Settlements

French couples may choose between two types of marriage settlements governing asset ownership after a divorce or inheritance: common property or separate property. A cooperative model considers the marriage contract as a means of providing for widowhood of the less endowed spouse. A second model addresses the probability of divorce and the production of a marriage good. The common property contract then becomes a means of inducing the wife to invest in the marriage good. Choice of contract, labor supply and fertility are simultaneous. Empirically we find that characteristics of the spouses such as relative age or differences in endowments influence the choice. So do the expected number of children and the wife's labor supply decision. This last decision is also shown to be influenced by the chosen settlement, while fertility is not.
JEL classification : J 12; J 4; K 12     

Common Pool Games are Convex Games

For the class of cooperative common pool games the paper focuses on the question of how, during the preplay negotiation process, the ability of coalitions to enforce their claims imposes externalities on the opposition by having an impact on the jointly produced resource. One of our main results is that common pool games are clear games. Based on this result we are able to derive sufficient conditions for the convexity of the characteristic function, which establishes the second main result in the paper, namely that cooperative common pool games are characterized by increasing returns with respect to the coalition size.     

“三农”问题与利益集团博弈

目前,我国存在着不同的利益集团,在国家决策过程中,进行着激烈博弈。“三农”问题的形成,则在于农民作为一个利益集团,无法与其他利益集团展开平等博弈。文章首先分析了利益集团的形成背景及其划分;其次,提出了农民与其他利益集团博弈中决策均衡点的形成依据;最后,提出了决策均衡点的实现机制。     

股票市场操纵行为的微观机理分析

本文通过对操纵股票市场交易价格的行为进行理论实证分析,剖析这种现象发生的原因、条件和本质,分析操纵市场行为对社会效率的影响,提出了规范股票投资行为、提升市场投资价值的建议.     

论我国的无效婚姻制度

新中国建立后1950年的婚姻法与1980年的婚姻法对结婚、离婚从实体要件到程序要件均予以了具体规定，但均未明文规定无效婚姻制度。1963年最高人民法院的司法解释首次提到婚姻无效的问题，指出应“宣布重婚关系无效”。在司法实践中，由于对违法婚姻的效力问题缺乏明确的法律依据，法院一般将属于无效婚姻的诉讼按离婚案件处理。     

Manipulation through political endorsements

We study elections with three candidates under plurality voting. A candidate is a Condorcet loser if the majority of the voters place that candidate at the bottom of their preference rankings. We first show that a Condorcet loser might win the election in a three-way race. Next we introduce to the model an endorser who has private information about the true probability distribution of the preferences of the voters. Observable endorsements facilitate coordination among voters who may otherwise split their votes and lead to the victory of the Condorcet loser. When the endorser has an ideological bias towards one of the candidates, the coordination impact of endorsements remains unaltered, moreover the endorser successfully manipulates the outcome of the election in favor of his bias, even if his ideological bias is known by the voters. The results are true for any endorsement cost and any magnitude of bias as long as the electorate is large enough.     

Action-Graph Games

Representing and reasoning with games becomes difficult once they involve large numbers of actions and players, because the space requirement for utility functions can grow unmanageably. Action-Graph Games (AGGs) are a fully-expressive game representation that can compactly express utility functions with structure such as context-specific independence, anonymity, and additivity. We show that AGGs can be used to compactly represent all games that are compact when represented as graphical games, symmetric games, anonymous games, congestion games, and polymatrix games, as well as games that require exponential space under all of these existing representations. We give a polynomial-time algorithm for computing a player's expected utility under an arbitrary mixed-strategy profile, and show how to use this algorithm to achieve exponential speedups of existing methods for computing sample Nash equilibria. We present results of experiments showing that using AGGs leads to a dramatic increase in the size of games accessible to computational analysis.²     

博弈论的新发展:行为博弈论

标准博弈论在经济理性假设下分析博弈参与者如何在追求各自最优目标的同时实现均衡。但是,由于现实行为人是有限理性的,标准博弈论对实践的解释和指导受到限制。为了延伸博弈论对现实活动的解释,行为博弈论将实验经济学与标准博弈论相融合,在博弈实验的基础上,考察和解释标准理论推断与实验结果之间的差异,引入行为因素改进标准博弈论的基本假定,重构博弈分析模型,以求达到准确解读有限理性的行为人在现实约束中如何行动的目的。     

中国股票市场交易型的价格操纵研究

本文研究中国股票市场的交易型价格操纵问题。我们推广了Mei、Wu和Zhou(2005)的模型,研究在市场不允许卖空的条件下,交易型价格操纵发生的条件。我们的主要结果有:(1)非充分理性投资者的存在和有限套利的制约是交易型价格操纵获利的重要原因,投机者套利能力越弱,操纵者的价格操纵越容易获利;(2)当市场中投机者的总禀赋大于0时,即使不允许卖空,价格操纵者依然可以操纵价格来获得利润;(3)如果市场监管者无法杜绝操纵者通过对敲等手段来拉抬股价,则在市场中引入卖空机制反而可以减小股价对基本面的偏离程度,从而在某种程度上限制操纵者操纵股价的空间;(4)在股价被操纵的过程中,存在一个建仓期和抛盘期;操纵期内换手率更高、股价波动更大;在建仓期,回报率与换手率,换手率与回报波动率之间存在正相关关系;(5)我们利用中国股市的数据检验了我们的结论,发现理论结果和实证数据非常吻合。     

Games of Status

A status game is a cooperative game in which the outcomes are rank orderings of the players. They are a good model for certain situations in which players care about how their "status" compares with that of other players.
We present several formal models within this class. Included are authoritarian status games (where coalitions may assign positions in the rank ordering to nonmembers) and oligarchic status games (where they are unableto do so). We consider the issues of a value concept for authoritarian games and that of core existence for oligarchic games. We then add a transferable resource to the models, obtaining "games of wealth and status."
Finally, we consider an interesting variant, called a "secession game," where coalitions have the right to secede from the grand coalition and form their own smaller "subsocieties," each with its own hierarchy.     

Knowledge Games

The subject of epistemic logic is firmly entrenched in game theory, including the analysis of common knowledge and of public announcements, such as in 'hat problems'. How to analyse communications to sub groups of the public, and the effects of such common knowledge of a subgroup on the information state of a larger group, has only recently come into fruition. Knowledge games are introduced to provide a comfortably concrete vehicle for the study of such interactions. This paper introduces the concepts of knowledge game, deal of cards, knowledge game state, game action, and action execution. A deal of cards is a function from cards to players. A knowledge game state is represented by a pointed multiagent S5 model on the set of card deals where all players hold the same number of cards as in the actual deal. A game action combines a question with an answer, and is represented by a pointed multiagent S5 frame on the set of possible answers. The execution of a game action in a knowledge game state corresponds to the computation of a pointed multiagent S5 model that is a restriction of the direct product of the corresponding action frame and game model.     

Ambiguous Games

This paper introduces ambiguous games, a modification of the normal form that allows the presence of vagueness in players' beliefs over the opponents' choice of strategies. An appropriate notion of equilibrium is presented, and a general existence result is proved. Journal of Economic Literature Classification Numbers: C72, D81.     

Network Games

In contexts ranging from public goods provision to information collection, a player's well-being depends on his or her own action as well as on the actions taken by his or her neighbours. We provide a framework to analyse such strategic interactions when neighbourhood structure, modelled in terms of an underlying network of connections, affects payoffs. In our framework, individuals are partially informed about the structure of the social network. The introduction of incomplete information allows us to provide general results characterizing how the network structure, an individual's position within the network, the nature of games (strategic substitutes vs. complements and positive vs. negative externalities) and the level of information shape individual behaviour and payoffs.     

Manipulation and the Pareto rule

This paper examines rules that map preference profiles into choice sets. There are no agendas other than the entire set of alternatives. A rule is said to be “manipulable” if there is a person i, and a preference profile, such that i prefers the choice set obtained when he is dishonest to the one obtained when he is honest. It is “nonmanipulable” if this can never happen. The paper indicates how preferences over choice sets might be sensibly derived from preferences over alternatives, and discusses seven different notions of manipulability associated with seven different assumptions about preferences over sets of alternatives. The paper has two sections of results. In the first I show that the Pareto rule, that is, the rule that maps preference profiles into corresponding sets of Pareto optima, is nonmanipulable in four of the seven senses of manipulability, and manipulable in three of them. In the second section, I examine this conjecture: If an arbitrary rule is nonmanipulable and nonimposed, and if indifference is disallowed, then every choice set must be contained in the set of Pareto optima. The conjecture is true under the strongest definition of nonmanipulability.     

Manipulation of endowments and sunspot equilibria

We study the connection between occurrence of manipulation via reallocating endowments by coalitions and sunspot equilibria. The uncertainty about which coalition will form introduces extrinsic uncertainty into the economy. Under certain conditions, manipulation of endowments by coalitions can occur if and only if sunspots matter. We would like to thank Bill Ethier, Atsushi Kajii, Cuong Le Van, Karl Shell, Koji Shimomura, Nicholas Yannelis, an anonymous referee, as well as seminar participants at the Second Asian General Equilibrium Theory Workshop, 2005, Tokyo; Workshop on Uncertainty and Information, IMS, NUS, 2005; Kobe Institute of Economic Research; Public Economic Theory 2005 Conference, Marseille; and the South and South East Asia Econometric Society Meetings, 2006, Chennai for helpful discussions and comments.     

Correlated Equilibrium in Stochastic Games

We study the existence of uniform correlated equilibrium payoffs in stochastic games. The correlation devices that we use are either autonomous (they base their choice of signal on previous signals, but not on previous states or actions) or stationary (their choice is independent of any data and is drawn according to the same probability distribution at every stage). We prove that any n-player stochastic game admits an autonomous correlated equilibrium payoff. When the game is positive and recursive, a stationary correlated equilibrium payoff exists. Journal of Economic Literature Classification Numbers: C72, C73.