on the robustness of equilibrium refinements abstract the philosophy of equilibrium refinements is that the analyst if he knows things about the structure of the game can reject some nash equilibria as unreasonable the word know in the preceding sentence deserves special emphasis if in a fixed game the analyst can reject a particular equilibrium outcome but he cannot do so for games arbitrarily close by then he may have second thoughts about rejecting the outcome we consider several notions of distance between games and we characterize their implications for the robustness of equilibrium refinements

rational panics and stock market crashes abstract this paper offers an explanation for stock market crashes which focuses on the role of rational but uninformed traders we show that uninformed traders can precipitate a price crash because as prices decline they surmise that informed traders received negative information which leads them to reduce their demand for assets and drive the price of stocks even lower the model yields several implications such as that crashes can occur even when the fundamentals are strong and that the magnitude of the crash depends on the fraction of uninformed investors and the amount of unsophisticated passive investing present in the market

unanimous rules in the laboratory we study the information aggregation properties of unanimous voting rules in the laboratory in line with theoretical predictions we find that majority rule with veto power dominates unanimity rule we also find that the strategic voting model is a fairly good predictor of subject behavior finally we exploit a framing effect to study how the presence of less sophisticated agents affects veto s welfare properties

voting on majority rules political economy models usually take as given the rules which govern the political decision making with the simple majority rule being the most popular model in this paper we develop a simple yet powerful positive model where the majority rule governing future elections is itself chosen in an election we observe a large variety of majority rules governing elections in the real world on the one side referenda are usually decided by a simple majority at the other extreme many international organizations require unanimity in votes among the member states in the european union s council of ministers some proposals require only a simple majority some a supermajority of about 71 62 votes out of 87 and some require unanimous consent 1 explicit supermajorities 2 are required in most countries for a change of the constitution but in some u s states also for a tax raise even more important could be what we might call implicit supermajorities in parliamentary systems with a strong committee organization a legislative proposal usually needs the support of both the respective committee and the house in parliamentary systems with two chambers certain legislative proposals need the support of both chambers 3 previous rationalizations of qualified majority rules focus on the problem of condorcet cycles under simple majority rule in n dimensional elections and on commitment problems see our literature review below our model presents a new rationale for rules requiring qualified majorities in elections we analyse an overlapping generations model of voting on reform opportunities which we model as similar to investment projects at first there is a cost and then there are benefits since voters have a finite lifetime old voters will be less keen on reforms

political bias and war we examine the incentives for countries to go to war as they depend on the comparison between how much their pivotal decision makers have at risk and how much they stand to gain from a war how this ratio compares to the country at large is what we term political bias if there is no political bias then there are always payments that one country would like to make to the other that will avoid a war in the presence of commitment or enforceability of peace treaties if there is a bias on the part of one or both countries then war can result and in some cases cannot be prevented by any transfer payments we examine how war technology and relative wealth levels interact with political bias in determining whether countries make transfers go to war and form alliances our results shed some new light on the uneven contender paradox and the interpretation of the democratic peace

majority rules and incentives a club s majority rule defines the number of members that must approve a policy proposed to replace the status quo since the majority rule thus dictates the extent to which winners must compensate losers it also determines the incentives to invest in order to become a winner of anticipated projects if the required majority is large members invest too little because of a holdup problem if it is small members invest too much in order to become a member of the majority coalition to balance these opposing forces the majority rule should increase in the project s value and the club s enforcement capacity but decrease in the heterogeneity in preferences externalities can be internalized by adjusting the rule with heterogeneity in size or initial conditions votes should be appropriately weighted or double majorities required

on the justice of decision rules which decision rules are the most efficient which are the best in terms of maximin or maximax we study these questions for the case of a group of individuals faced with a collective choice from a set of alternatives a key message from our results is that the set of optimal decision rules is well defined particularly simple and well known the class of scoring rules we provide the optimal scoring rules for the three different ideals of justice under consideration utilitarianism efficiency maximin and maximax the optimal utilitarian scoring rule depends crucially on the probability distribution of the utilities the optimal maximin respectively maximax scoring rule takes the optimal utilitarian scoring rule and applies a factor that shifts it towards negative voting respectively plurality voting

information aggregation rationality and the condorcet jury theorem the condorcet jury theorem states that majorities are more likely than any single individual to select the better of two alternatives when there exists uncertainty about which of the two alternatives is in fact preferred most extant proofs of this theorem implicitly make the behavioral assumption that individuals vote sincerely in the collective decision making a seemingly innocuous assumption given that individuals are taken to possess a common preference for selecting the better alternative however in the model analyzed here we find that sincere behavior by all individuals is not rational even when individuals have such a common preference in particular sincere voting does not constitute a nash equilibrium a satisfactory rational choice foundation for the claim that majorities invariably do better than individuals therefore has yet to be derived

voting for voters a model of electoral evolution we model the decision problems faced by the members of societies whose new members are determined by vote we adopt a number of simplifying assumptions the founders and the candidates are fixed the society operates for k periods and holds elections at the beginning of each period one vote is sufficient for admission and voters can support as many candidates as they wish voters assess the value of the streams of agents with whom they share the society while they belong to it in spite of these simplifications we show that interesting strategic behavior is implied by the dynamic structure of the problem the vote for friends may be postponed and it may be advantageous to vote for enemies we discuss the existence of different types of equilibria in pure strategies and point out interesting equilibria in mixed strategies

collusion and price rigidity we consider an in nitely repeated bertrand game in which prices are publicly observed and each rm receives a privately observed i i d cost shock in each period we focus on symmetric perfect public equilibria sppe wherein any punishments are borne equally by all rms we identify a tradeoff that is associated with collusive pricing schemes in which the price to be charged by each rm is strictly increasing in its cost level such fully sorting schemes offer efficiency bene ts as they ensure that the lowest cost rm makes the current sale but they also imply an informational cost distorted pricing and or equilibrium path price wars since a higher cost rm must be deterred from mimicking a lower cost rm by charging a lower price a rigid pricing scheme where a rm s collusive price is independent of its current cost position sacri ces efficiency bene ts but also diminishes the informational cost for a wide range of settings the optimal symmetric collusive scheme requires i the absence of equilibrium path price wars and ii a rigid price if rms are sufficiently impatient however the rigid pricing scheme cannot be enforced and the collusive price of lower cost rms may be distorted downward in order to diminish the incentive to cheat when the model is modi ed to include i i d public demand shocks the downward pricing distortion that accompanies a rm s lower cost realization may occur only when current demand is high

voting blocs party discipline and party formation abstract i study the strategic incentives to coordinate votes in an assembly coalitions form voting blocs acting as single players and affecting the policy outcome in an assembly with two exogenous parties i show how the incentives to accept party discipline depend on the types of the agents the sizes of the parties and the rules the blocs use to aggregate preferences in a game of fully endogenous party formation i find sufficient conditions for the existence of equilibria with one bloc two blocs and multiple blocs

a volatility based theory of fiscal union desirability abstract heterogeneous countries may rationally choose to form a currency union first and a fiscal union later we find and illustrate empirically for the emu countries reasonable volatility conditions under which this sequencing in the deepening process is indeed rationalizable changes in the distribution of expected income shocks require a reassignment of political weights to restore unanimous support for an added fiscal dimension the bargaining space depends on countries relative income size and cross correlation of shocks

correlated equilibrium as an expression of bayesian rationality if it is common knowledge that the players in a game are bayesian utility maximizers who treat uncertainty about other players actions like any other uncertainty then the outcome is necessarily a correlated equilibrium random strategies appear as an expression of each player s uncertainty about what the others will do not as the result of willful randomization use is made of the common prior assumption according to which differences in probability assessments by different individuals are due to the different information that they have where information may be interpreted broadly to include experience upbringing and genetic makeup copyright 1987 by the econometric society

relational incentive contracts standard incentive theory models provide a rich framework for studying informational problems but assume that contracts can be perfectly enforced this paper studies the design of self enforced relational contracts i show that optimal contracts often can take a simple stationary form but that self enforcement restricts promised compensation and affects incentive provision with hidden information it may be optimal for an agent to supply the same inefficient effort regardless of cost conditions with moral hazard optimal contracts involve just two levels of compensation this is true even if performance measures are subjective in which case optimal contracts terminate following poor performance jel c73 d82 l14

towards a renaissance of economic theory in his penetrating essay theory and experiment vernon smith observes that subject behavior often diverges from game theoretic predictions and asserts that minor fudging with theory is unlikely to solve our problems because circumstances unknown to us are responsible for the explanatory failures of neoclassical economic theory i deal precisely with these issues in thebounds of reason 2009a my remarksheredrawupon several themes fromthis book relevant to specifying a refocused research agenda for the study of human strategic interaction the core of economic theory is the rational actor model which holds that individuals have preferences over outcomes beliefs called subjectivepriors linking choices to the relativeprobability of alternativeoutcomes and theymaximize their expected payoffs given these preferences and beliefs subject towhatevermaterial informational and other constraints they face many observers consider the experimental work of daniel kahneman and others kahneman et al 1982 gigerenzer and todd 1999 as destructive of the rational actormodel in fact however their research has considerably strengthened the rational actor model s explanatory power albeit at the expense of increasing its complexity gintis 2009a chs 1 and 12 most important these studies have shown the value of modeling using heuristics that conserve on information processing and of including the current state physiological temporal and ownership of the individual as an argument of the preference ordering in the 1980s the core of economic theory was extended to include game theory viewed as the theory of the strategic interaction of bayesian rational actors game theory has become a centerpiece of microeconomic theory alongside the traditional walrasian model of general market equilibrium it is important to note however that this exalted position is quite recent the textbooks that expound the received wisdom of today s practicing economists were written in the early years of the game theory revival between 1988 and 1995 these textbooks include misconceptions promulgated in the 1980s that have been transmitted to the current generation of economists as i shall show some of these misconceptions have been repaired in more recent contributions to game theory contemporary experimentalists however generally rely on the more traditional body of outdated theory i here rely on more recent theoretical contributions especially those of robert aumann and adam brandenburger and their coworkers to bring game theory up to date i then argue that despite their analytical power game theory and the rational actor model provide only part of the theoretical toolkit needed to explain human strategic interaction moreover because individuals bring much of the complexity of society into the controlled conditions of the laboratory game theory and the rational actor model are insufficient to explain experimental results concretely i suggest that a these analytical tools must be supplemented by what i term the psycho social theory of norms b the correlated equilibrium should replace

self enforcing voting in international organizations some international organizations are governed by unanimity rule some others by a majority system still others have moved from one system to the other over time the existing voting models have a difficult time explaining the observed variation in governance mode and in particular the widespread occurrence of the unanimity system we present a model whose main departure from standard voting models is that there is no external enforcement mechanism each country is sovereign and cannot be forced to follow the collective decision or in other words the voting system must be self enforcing the model yields unanimity as the optimal system for a wide range of parameters and delivers rich predictions on the variation in the mode of governance both across organizations and over time we thank james anderson matt jackson francois maniquet guido tabellini and jean tirole for very helpful comments arnaud costinot provided excellent research assistance we also bene

choosing how to choose self stable majority rules and constitutions constitutional arrangements affect the decisions made by a society we study how this effect leads to preferences of citizens over constitutions and ultimately how this has a feedback that determines which constitutions can survive in a given society constitutions are stylized here to consist of a voting rule for ordinary business and possibly a different voting rule for making changes to the constitution we define an equilibrium notion for constitutions called self stability whereby under the rules of a self stable constitution the society would not vote to change the constitution we argue that only self stable constitutions will endure we prove that self stable constitutions always exist but that most constitutions even very prominent ones may not be self stable for some societies we show that constitutions where the voting rule used to amend the constitution is the same as the voting rule used for ordinary business are dangerously simplistic and there are many societies for which no such constitution is self stable we conclude with a characterization of the set of self stable constitutions that use majority rule for ordinary business

rationalizable strategic behavior and the problem of perfection this paper explores the fundamental problem of what can be inferred about the outcome of a noncooperative game from the rationality of the players and from the information they possess the answer is summarized in a solution concept called rationalizability strategy profiles that are rationalizable are not always nash equilibria conversely the information in an extensive form game often allows certain unreasonable nash equilibria to be excluded from the set of rationalizable profiles a stronger form of rationalizability is appropriate if players are known to be not merely rational but also cautious what constitutes rational behavior in a noncooperative strategic situation this paper explores the issue in the context of a wide class of finite noncooperative games in extensive form the traditional answer relies heavily upon the idea of nash equilibrium nash 17 the position developed here however is that as a criterion for judging a profile of strategies to be reasonable choices for players in a game the nash equilibrium property is neither necessary nor sufficient some nash equilibria are intuitively unreasonable and not all reasonable strategy profiles are nash equilibria the fact that a nash equilibrium can be intuitively unattractive is well known the equilibrium may be imperfect introduced into the literature by selten 20 the idea of imperfect equilibria has prompted game theorists to search for a narrower definition of equilibrium while this research some of which will be discussed here has been extremely instructive it remains inconclusive theorists often agree about what should happen in particular games but to capture this intuition in a general solution concept has proved to be very difficult if this paper is successful it should make some progress in that direction the other side of the coin has received less scrutiny can all non nash profiles really be excluded on logical grounds i believe not the standard justifications for considering only nash profiles are circular in nature or make gratuitous assumptions about players decision criteria or beliefs the following discussion of these points is extremely brief due to space constraints more detailed arguments may be found in pearce 18

efficiency in games with markovian private information we study repeated bayesian games with communication and observable actions in which the players privately known payoffs evolve according to an irreducible markov chain whose transitions are independent across players our main result implies that generically any pareto efficient payoff vector above a stationary minmax value can be approximated arbitrarily closely in a perfect bayesian equilibrium as the discount factor goes to 1 as an intermediate step we construct an approximately efficient dynamic mechanism for long finite horizons without assuming transferable utility publication abstract

incomplete social contracts there is a long normative social contract tradition that attempts to characterize ex post income inequalities that are agreeable to all behind a veil of ignorance this paper takes a similar normative approach to characterize social decision making procedures it is shown that quite generally some form of majority voting is preferred to unanimity behind a veil of ignorance whenever society faces deadweight costs in making compensating transfers deviations from unanimity or ex post pareto optimality are ex ante efficient to the extent that they economize on costly compensating transfers put another way the optimal decision rule trades off the benefits of minority protection and those from greater flexibility jel h11 g33 g34 d63 p16 p48

short sales constraints and price discovery evidence from the hong kong market short sales practices in the hong kong stock market are unique in that only stocks on a list of designated securities can be sold short by analyzing the price effects following the addition of individual stocks to the list we find that short sales constraints tend to cause stock overvaluation and that the overvaluation effect is more dramatic for individual stocks for which wider dispersion of investor opinions exists these findings are consistent with miller s 1977 intuition and other optimism models we also document higher volatility and less positive skewness of individual stock returns when short sales are allowed the question of how short sales impact capital markets is highly controversial with short sale regulations varying widely across countries and capital markets 1 although short selling has been carried out for years in major financial markets around the world its effects on market efficiency especially on pricing efficiency remain of interest to financial researchers miller 1977 theorizes that in the presence of short sales constraints security prices tend to reflect a more optimistic valuation than the average opinion of potential investors and thus tend to be upward biased this overvaluation argument is based on two conditions 1 a security s short sales are either prohibited or costly and 2 investors have heterogeneous beliefs or information about the security s value the underlying intuition is quite straightforward pessimistic investors are forced to sit out of the market when short sales are not available and thus some negative information is not reflected in prices enabling enthusiastic buyers to bid prices above the level that average investors perceive as fair this argument has significant implications for market efficiency theories since one of the major functions of capital markets is price discovery indeed an efficient market should be a market in which prices always

explaining institutional change policy areas outside options and the bretton woods institutions i propose and test a theoretical framework that explains institutional change in international relations like firms in markets international institutions are affected by the underlying characteristics of their policy areas some policy areas are prone to produce institutions facing relatively little competition limiting the outside options of member states and impeding redistributive change in comparison institutions facing severe competition will quickly reflect changes in underlying state interests and power to test the theory empirically i exploit common features of the bretton woods institutions the international monetary fund and world bank to isolate the effect of variation in policy area characteristics the empirical tests show that despite having identical membership and internal rules bargaining outcomes in the bretton woods institutions have diverged sharply and in accordance with the theory

short sales and stock price crash risk evidence from an emerging market abstract using a regulatory change in china as an exogenous shock we find that the removal of short sales constraints increases stock price crash risk this relation is attenuated when firms suffer less from information asymmetry highlighting the effect of interaction between uninformed and informed investors

optimal cartel equilibria with imperfect monitoring abstract there exist optimal symmetric equilibria in the green porter model 4 8 having an elementary intertemporal structure such an equilibrium is described entirely by two subsets of price space and two quantities the only production levels used by firms in any contingency the central technique employed in the analysis is the reduction of the repeated game to a family of static games

power control and the logic of substitution in institutional design the case of international climate finance how do powerful states control international organizations ios in contrast to the conventional wisdom that treats weighted voting rules as the primary means that powerful states use to codify their asymmetric control in institutional design we propose that funding rules are equally important our framework develops a logic of substitution whereby permissive earmark rules that allow donors to stipulate how their contributions to an io are used are a design substitute for weighted voting from wealthy states perspective whether asymmetric control is incorporated in design through voting or funding rules depends on whether egalitarian norms emphasizing political and legal equality or shareholder norms emphasizing influence commensurate with financial power govern voting and representation rights at the io focusing on the domain of climate finance we demonstrate that weighted voting rules are used at international climate finance institutions icfis associated with multilateral development banks but that wealthy states pursued permissive earmark rules at icfis within the united nations system where egalitarian norms are strong in this way powerful donors can exert control over resource allocation even when developing states appear to hold equal influence on governing bodies in addition to providing a reassessment of how power translates into control at ios our framework offers insight into forum shopping behavior and sheds light on substitution dynamics that involve other dimensions of design across a range of issue areas

insider trading in a rational expectations economy it is often argued that efficiency considerations require society to freely permit insider trading in this article an opposing efficiency argument is formalized the model incorporates an investment stage followed by a trading stage if outsiders expect insiders to take advantage of them in trading outsiders will reduce their investment the insiders loss from this diminished investor confidence may more than offset their trading gains consequently a prohibition on insider trading may effect a pareto improvement insiders are made better off if they can precommit not to trade on their privileged information govemment regulation accomplishes exactly this jel 022 026 313 the traditional rationale articulated for insider trading regulation and other securities law is that such rules promote confidence in markets indeed president franklin d roosevelt justified the first major u s securities legislation by saying it should give impetus to honest dealing in securities and thereby bring back public confidence similar language is still invoked half a century later in connection with enforcement efforts against insider trading and in proposals for tightened stock

on 64 majority rule introduction d une definition de consensus social base sur deux restrictions une sur les preferences individuelles et l autre sur la distribution des preferences dans ce cas de consensus une regle de majorite a 64 presente de nombreuses proprietes interessantes par opposition aux regles de super majorite possedant des proprietes paradoxales comme les regles electorales americaines

common belief and the theory of games with perfect information abstract the statement it is common belief that player i is bayesian rational where bayesian rational means an expected utility maximizer is defined for two person games with perfect information it is shown that in most such games it is not possible for a theory so postulate the bayesian rationality of all players and to be common belief this bears directly upon the salience of standard solution concepts such as subgame perfect and sequential equilibria as well as upon the extensive form rationalizability theories of d bernheim econometrica 52 1984 1009 1028 and d pearce econometrica 52 1984 1029 1050 which rely heavily on the common belief of bayesian rationality journal of economic literature classification number c72

rational cooperation in the finitely repeated prisoner s dilemma experimental evidence this paper presents experiments designed to examine the sequential equilibrium reputation hypothesis in the finitely repeated prisoner s dilemma the authors test the hypothesis by controlling the subjects ability to build reputations and by manipulating their beliefs that their opponent is irrational or altruistic the responses of subjects strongly support the sequential equilibrium prediction the results also suggest an important role for homemade altruism that is a natural tendency to cooperate that subjects bring to the experiment from the outside the authors find that there may be no difference between the beliefs that an opponent is altruistic and the actual chance it is so copyright 1993 by royal economic society

centralized fiscal spending by supranational unions we study fiscal spending by supranational unions where participation is voluntary and countries bargain over contributions to and the allocation of a central budget since decisions are made by unanimity bargaining power over the allocation becomes a function of contributions which generically causes inefficiency in the presence of income asymmetry between member nations this link between the budget allocation and contributions explains patterns of inefficient spending in the eu e g why resources are diverted to low productivity projects in high income countries the option of veto creates a trade off between efficiency on the contributions margin and efficiency on the allocation margin

strategic delegation and voting rules abstract the selection of political representatives depends on the political system principals such as voters or districts may benefit by strategically electing representatives different from themselves while a status quo biased delegate may be a better negotiator an enthusiastic representative has a better chance of being included in the majority coalition a larger majority requirement leads to conservative delegation and hence a status quo bias a poor minority protection does the opposite through strategic delegation the political system also determines whether centralization or decentralization is beneficial

structuring international institutions for the efficient provisioning of global security this paper analyzes the issue of security provision by an alliance against the threat of a rogue nation proactive security effort by an alliance member is assumed to be non rival and non excludable so the results of the effort jointly accrue to every other member this effort has both positive and negative effects as security measures mitigate the threat but also involve loss of commercial benefits collateral damages and infringement on human rights in this paper i suggest an institutional structure for the alliance which would lead to the achievement of the efficient level of world security through multilateral participation

abiding by the vote between groups conflict in international collective action we analyze institutional solutions to international cooperation when actors have heterogeneous preferences over the desirability of the action and split into supporters and opponents all of whom can spend resources toward their preferred outcome we study how actors can communicate their preferences through voting when they are not bound either by their own vote or the outcome of the collective vote we identify two organizational types with endogenous coercive enforcement and find that neither is unambiguously preferable like the solutions to the traditional prisoners dilemma these forms require long shadows of the future to sustain we then show that cooperation can be sustained through a noncoercive organization where actors delegate execution to an agent even though this institution is costlier it does not require any expertise by the agent and is independent of the shadow of the future and thus is implementable when the others are not

rationality nash equilibrium and backwards induction in perfect information games we say that a player is certain of an event a if she assigns probability 1 to a there is common certainty cc of a if the event a occurred each player is certain of a each player is certain that every other player is certain of a and so forth it is shown that in a generic perfect information game the set of outcomes that are consistent with common certainty of rationality ccr at the beginning of the game coincides with the set of outcomes that survive one deletion of weakly dominated strategies and then iterative deletion of strongly dominated strategies thus the backward induction outcome is not the only outcome that is consistent with ccr in particular cooperation in rosenthal s 1981 centipede game and fighting in selten s 1978 chainstore game are consistent with ccr at the beginning of the game next it is shown that if in addition to ccr there is cc that each player assigns a positive probability to the true strategies and beliefs of the other players and if there is cc of the support of the beliefs of each player then the outcome of the game is a nash equilibrium outcome