new tests of qalys when health varies over time this paper performs new tests of the qaly model when health varies over time our tests do not involve confounding assumptions and are robust to violations of expected utility the results support the use of qalys at the aggregate level i e in economic evaluations of health care at the individual level there is less support for qalys the individual data are however largely consistent with a more general qaly type model that remains tractable for applications

simple strategy proof approximately walrasian mechanisms abstract this note provides an indirect analysis of the incentive properties of the walrasian mechanism it presents mechanisms under which truth telling is a dominant strategy in finite exchange economies in contrast to the walrasian mechanism and whose outcomes generically approximate walrasian ones for large economies these mechanisms provide new insights on the well know trade off between efficiency and incentive compatibility in finite economies journal of economic literature classification numbers d50 d71 d78

strategy proof exchange we consider the allocation of goods in exchange economies with a finite number of agents who may have private information about their preferences in such a setting standard allocation rules such as walrasian equilibria or rational expectations equilibria are not compatible with individual incentives we characterize the set of allocation rules which are incentive compatible or in other words the set of strategy proof social choice functions social choice functions which are strategy proof are those which can be obtained from trading according to a finite number of pre specified proportions the number of proportions which can be accommodated is proportional to the number of agents such rules are necessarily inefficient even in the limit as the economy grows

qalys and hyes under what conditions are they equivalent the paper examines what restrictions have to be imposed on the individual s preference structure for qalys and hyes to yield identical results it is shown that using qalys involves imposing three additional restrictions empirical evidence suggests that these restrictions cannot be expected to hold in all applications the main problem in using hyes appears to be practical an alternative index is proposed that may help to bridge the gap between qalys and hyes by combining to some extent the advantages of the two measures

continuity in auction design abstract j cremer and r p mclean econometrica56 1988 1247 1257 have shown that the auctioneer can extract all the surplus when the private valuations of bidders are not statistically independent the paper shows that this result does not necessarily arise under limited liability or risk aversion under limited liability and or risk aversion we prove that the functions corresponding to the auctionner s optimal expected gain and to the maximum total surplus are continuous in the space of possible information distributions thus by continuity the auctioneer wil not be able to extract all the rents when bidders private valuations are approximately independent

time preference the discounted utility model and health the constant rate discounted utility model is commonly used to represent intertemporal preferences in health care program evaluations this paper examines the appropriateness of this model and argues that the model fails both normatively and descriptively as a representation of individual intertemporal preferences for health outcomes variable rate discounted utility models are more flexible but still require restrictive assumptions and may lead to dynamically inconsistent behaviour the paper concludes by considering two ways of incorporating individual intertemporal preferences in health care program evaluations that allow for complementarity of health outcomes in different time periods

threshold strategy proofness on manipulability in large voting problems in voting problems where agents have lipschitz continuous utility functions on a multidimensional space of alternatives a voting rule is threshold strategy proof if any agent can obtain only a limited utility gain by not voting for a most preferred alternative if the number of agents is large enough for anonymous voting rules it is shown that this condition is not only implied by but is in fact equivalent to the influence of any single agent decreasing to zero as the number of agents grows if there are at least five agents the mean rule taking the average vote is shown to be the unique anonymous and unanimous voting rule that meets a lower bound with respect to the number of agents needed to obtain threshold strategy proofness

informational smallness and the scope for limiting information rents abstract for an incomplete information model of public good provision with interim participation constraints we show that efficient outcomes can be approximated with approximately full surplus extraction when there are many agents and each agent is informationally small the result holds even if agents payoffs cannot be unambiguously inferred from their beliefs the contrary result of neeman z neeman the relevance of private information in mechanism design j econ theory 117 2004 55 77 rests on an implicit uniformity requirement that is incompatible with the notion that agents are informationally small because there are many other agents who have information about them

implementation in differential information economies abstract we consider the problem of implementation of social choice correspondences in differential information economies we provide necessary conditions for implementation and slightly stronger conditions which are sufficient to guarantee implementation

approximately competitive equilibria in large finite economies abstract we consider exchange economies where each consumer may report or act according to any demand function provided that there exist situations that the consumer finds plausible in which the reported demand performs at least as well as the true demand we identify conditions under which as the size of the economy increases all the market clearing prices and allocations of the reported economy approximate the competitive equilibria of the true economy journal of economic literature classification numbers d51 d82

a new axiomatic approach to the evaluation of population health in this paper we explore the implications of normative principles for the evaluation of population health we formalize those principles as axioms for social preferences over distributions of health for a given population we single out several focal population health evaluation functions which represent social preferences as a result of combinations of those axioms our results provide new rationale for popular theories in health economics such as the unweighted aggregation of quality adjusted life years qalys or healthy years equivalents hyes and generalizations of the two aimed to capture concerns for distributive justice without resorting to controversial assumptions on individual preferences

production and investment decisions under sunk cost and temporal uncertainty building on glenn johnson s asset fixity theory this article introduces sunk cost and temporal uncertainty in jorgenson s neoclassical theory of investment under the assumption of risk neutrality we show sunk cost and temporal risk affect the implicit rental value of capital and investment and entry exit decisions results suggest there are important interactions between sunk cost and the effects of temporal uncertainty on production behavior

linking life cycle assessment to bioeconomic modelling with positive mathematical programming an alternative approach to calibration abstract increased attention has been paid to extending the use of agricultural life cycle assessment by linking it to bioeconomic models with positive mathematical programming previous extension studies might have provided insufficient support to potential users e g policymakers in finding effective means of operating an agriculture industry in a sustainable manner this is partly a result of the fact that orthodox positive mathematical programming involves numerous calibration methods that reproduce the original land area allocation at the reference point implying that they generate as many simulation results as the number of calibration methods themselves to have more of an impact the present study proposed a procedure for using simulation results to determine a calibration method as an illustration the proposed procedure was applied to an upland cropping system in hokkaido japan it was observed that the selected calibration method outperformed the average cost method the method used most frequently in practice for the specified dataset the procedure suggested in the present study proved to be more flexible than previous approaches with respect to the selection process of calibration methods and it could be regarded as a step toward harmonizing the extended use of life cycle assessment with bioeconomic modelling implications for bioeconomic models and agricultural life cycle assessments are then discussed the present study adds a new analytical method to the existing knowledge on the extended use of life cycle assessment with bioeconomic models

on the possibility of informationally efficient markets this paper presents conditions for a resolution of the grossman stiglitz paradox of informationally efficient markets we display a market with asymmetric information where a privately revealing equilibrium obtains in a competitive framework and where incentives to acquire information are preserved as long as the correlation in traders valuations is not too large the equilibrium is efficient and the problems associated with fully revealing rational expectations equilibria are precluded without resorting necessarily to noise traders the robustness of the results to general information structures is established and the effect of market power is examined in a large market approximation to the competitive economy the model is applied to explain changes in bidding behavior in central bank liquidity auctions in the crisis period jel d82 d84 g14 e59

asymmetric enforcement of cooperation in a social dilemma we use a public good experiment to analyze behavior in a decentralized asymmetric punishment institution the institution is asymmetric in the sense that players differ in the effectiveness of their punishment at the aggregate level we observe remarkable similarities between outcomes in asymmetric and symmetric punishment institutions controlling for the average punishment effectiveness of the institutions we find that asymmetric punishment institutions are as effective in fostering cooperation and are as efficient as symmetric institutions at the individual level we find that players with higher punishment effectiveness contribute similar amounts to the public account but have higher earnings and punish more than their weak counterparts

on the failure of core convergence in economies with asymmetric information in interim economies with asymmetric information we show that the coarse core of wilson 1978 does not converge to price equilibrium allocations as the economy is replicated this failure of core convergence is a basic consequence of asymmetric information and extends to any reasonable notion of either interim core or price equilibrium

tests of utility independence when health varies over time in the conventional quality adjusted life year qaly model people s preferences are assumed to satisfy utility independence when health varies over time utility independence implies that the value attached to a health state is independent of the health state that arise before or after it two separate studies were conducted involving a total of 155 respondents in study one we conducted five tests of utility independence using a standard gamble question three of the tests of utility independence were repeated in study two after randomisation was introduced in order to take account of possible ordering effects utility independence holds in the majority of cases examined here and so our work generally supports the use of utility independence to derive more tractable models

surplus extraction and competition a competitive economy is studied in which sellers offer alternative direct mechanisms to buyers who have correlated private information about their valuations in contrast to the monopoly case where sellers charge entry fees and extract all buyers surplus it is shown that in the unique symmetric equilibrium with competition sellers hold second price auctions with reserve prices set equal to their cost most important it is a best reply for sellers not to charge entry fees of the kind normally used to extract surplus even though it is feasible for them to do so

market power and information revelation in dynamic trading we study a strategic model of dynamic trading where agents are asymmetrically informed over common value sources of uncertainty there is a continuum of buyers and a finite number n of sellers all buyers are uninformed while at least one seller is privately informed about the true state of the world when n 1 full information revelation never occurs in equilibrium and the only information transmission happens in the first period with n 1 the outcome depends both on the structure of the sellers information and even more importantly on the intensity of competition allowed by the existing trading rules when there is intense competition absence of clienteles information is fully and immediately revealed to the buyers in every equilibrium for n large enough regardless of the number of informed sellers on the other hand for trading arrangements characterized by less intense forms of competition presence of clienteles for any n we always have equilibria where information is never fully revealed moreover in that case when only one seller is informed for many parameter configurations there are no equilibria with full information revelation even for large n jel c72 c78 d82 d83

the efficiency of competitive mechanisms under private information we consider the efficiency properties of exchange economies where privately informed traders behave strategically specifically a competitive mechanism is any mapping of traders reports about their types to an equilibrium price vector and allocation of the reported economy in our model some traders may have non vanishing impact on prices and allocations regardless of the size of the economy although truthful reporting by all traders cannot be achieved we show that given any desired level of approximation there is n such that any bayesian nash equilibrium of any competitive mechanism of any private information economy with n or more traders leads with high probability to prices and allocations that are close to a competitive equilibrium of the true economy in particular allocations are approximately efficient a key assumption is that there is small probability that traders behave non strategically

trade with heterogeneous prior beliefs and asymmetric information no trade theorems have shown that new information will not lead to trade when agents share the same prior beliefs this paper explores the structure of no trade theorems with heterogeneous prior beliefs it is shown how different notions of efficiency under asymmetric information ex ante interim ex post are related to agents prior beliefs as well as incentive compatible and public versions of those efficiency concepts these efficiency results are used to characterize necessary and sufficient conditions on agents beliefs for no trade theorems in different trading environments

search adverse selection and market clearing we examine a dynamic decentralized trading model with infinitesimal sellers and buyers to investigate whether or not the market fails to clear in the limit of search friction vanishing a seller who has private information about product quality and a buyer are matched to bargain over price they form a long term relationship if they reach agreement they return to the matching pool if they fail to agree or the existing relationship is dissolved the market fails to clear if and only if the ratio of agents patience over the dissolution rate exceeds a threshold

monotonicity and rationalizability in a large first price auction this paper proves that the monotonicity of bidding strategies together with the rationality of bidders implies that the winning bid in a first price auction converges to the competitive equilibrium price as the number of bidders increases wilson 1977 instead of analysing the symmetric nash equilibrium we examine rationalizable strategies bernheim 1984 pearce 1984 among the set of monotonic bidding strategies to prove that any monotonic rationalizable bidding strategy must be within a small neighbourhood of the truthful valuation of the object conditioned on the signal received by the bidder we obtain an information aggregation result similar to that of wilson 1977 while dispensing with almost all symmetric assumptions and using a milder solution concept than the nash equilibrium in particular if every bidder is ex ante identical then any rationalizable bidding strategy must be within a small neighbourhood of the symmetric nash equilibrium in a symmetric first price auction the symmetry of outcomes is implied rather than assumed copyright 2005 wiley blackwell

multiple policy instruments for sustainable water management in crop production a modeling study for the chinese aksu tarim region china s crop production sector faces severe water scarcity issues previous research has shown that effective water conservation policies exert strongly negative impacts on agricultural production and farmers income which make them politically unfeasible under chinese conditions to highlight ways out of this dilemma the present study tests three alternative water policies complemented by supportive agricultural policies to reduce the trade offs between water conservation and rural development policy goals using the case of the extremely arid aksu tarim region in northwest china a regional supply model is developed which serves as the analysis framework applied as stand alone water policies irrigated area tax water quota and water pricing differ clearly in effectiveness and efficiency combined with agricultural policies subsidies into multiple policy instruments the price based and quota based instruments mitigate the negative impacts on rural development goals targeting a water conservation rate of 20 the tested multiple policies perform alike on the level of the entire study region cotton production decreases by 15 cereals production remains stable and regional income decreases by 13 however at the sub regional level the impacts on water conservation production and income differ significantly between the alternative policy instruments and sub regions constituting a crucial challenge for practical water policy implementation

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

implementation in economies with a continuum of agents we study a general implementation problem for exchange economies with a continuum of players and private information and test the robustness of the results for sequences of approximating finite economies assuming that the designer knows the distribution of the characteristics in the economy we consider continuous and unique implementation in both its equilibrium and dominant strategies versions and obtain results for general self selective first and second best allocations an upper hemicontinuity property of bayesian equilibria of approximating economies for continuous mechanisms is demonstrated using this we can for example conclude that if a given continuous mechanism implements uniquely a walrasian allocation in the continuum economy then all bayesian equilibria of large approximation economies will with probability close to one yield an allocation which is almost ex post pareto optimal

feasible and continuous implementation there has been a great deal of research in recent years investigating the question of whether or not there exist institutions game forms for which the set of equilibria will coincide with the set of walrasian equilibria in this paper we show the existence of a game form that is feasible both for equilibrium and disequilibrium strategies continuous and for which the set of nash equilibria coincides with the set of constrained walrasian equilibria for all pure exchange economies the game form allows agents to behave strategically both with respect to their preferences and their initial endowments

a semi separable utility function for health profiles under expected utility the individual preferences over lotteries on health profiles can be represented either by a multiplicative utility function when mutual utility independence is claimed or an additive one known as qaly when it is claimed additive independence in this paper we impose a weaker condition i e utility independence with respect to the initial health states of an individual decision maker initial independence and we derive a semi separable utility function in addition we assess its parameters by a standard gamble procedure our results could be useful in cost utility analysis for carrying out health care program evaluations

private information in large economies this paper examines the effect of private information in large economies we show that in a model with stochastic information structures the restrictions imposed on allocations by the presence of private information disappear in large economies we also show that for a large class of direct mechanisms the incentive for any agent to falsely report private information goes to zero as the number of agents becomes large these results provide an informational smallness analog to existing quantity smallness limiting results in the literature

asymptotic efficiency in large exchange economies with asymmetric information the authors provide conditions on an exchange economy with asymmetric information that guarantee that when the economy is replicated sufficiently often there will be an allocation that is incentive compatible individually rational and nearly efficient the main theorem covers both the case in which aggregate uncertainty remains when the economy is replicated and the case in which replication eliminates aggregate uncertainty in addition the authors demonstrate how their theorem does or does not apply to standard asymmetric information problems such as the buyer s bid double auction problem akerlof s lemons problem and insurance with asymmetric information copyright 1992 by the econometric society

imperfect competition and efficiency in lemons markets this article studies the impact of competition on the degree of inefficiency in lemons markets more precisely we characterise the second best mechanism i e the optimal mechanism with private information in a stylised lemons market with finite numbers of buyers and sellers we then study the relationship between the degree of efficiency of the second best mechanism and market competitiveness a general message of our results is that increasing competition may not help lemons markets in some circumstances moreover increasing competition beyond a certain degree increases the distance between the first best and second best levels of efficiency

multiattribute utility theory without expected utility foundations methods for determining the form of utilities are needed for the implementation of utility theory in specific decisions an important step forward was achieved when utility theorists characterized useful parametric families of utilities and simplifying decompositions of multiattribute utilities the standard development of these results is based on expected utility theory which is now known to be descriptively invalid the empirical violations of expected utility impair the credibility of utility assessments this paper shows however that parametric and multiattribute utility results are robust against the major violations of expected utility they retain their validity under nonexpected utility theories that have been developed to account for actual choice behavior to be precise characterizations of parametric and multiattribute representations are extended to rank dependent utility state dependent utility choquet expected utility and prospect theory

incomplete information incentive compatibility and the core abstract we consider an exchange economy in which agents possess private information at the time of engaging in state contingent contracts while communication of private information is permitted the true information state is not verifiable the enforcement of contracts is therefore limited by incentive compatibility constraints we formalize a notion of the core for such an economy our analysis can be viewed as an attempt to incorporate incentive compatibility in the coarse core of r wilson 1978 econometrica46 807 816 or as an attempt to introduce coalitional contracts in the notion of incentive efficiency of b holmstrom and r myerson 1983 econometrica51 1799 1819 while there are some special cases in which the incentive compatible core is non empty our main result shows that is not generally true journal of economic literatureclassification numbers c71 c72 d51

correlated information and mechanism design in models of asymmetric information possession of private information leads to rents for the possessors this induces mechanism designers to distort away from efficiency the authors show that this is an artifact of the presumption that information is independently distributed rent extraction in a large class of mechanism design games is analyzed and a necessary and sufficient condition for arbitrarily small rents to private information is provided additionally the two person bargaining game is shown to have an efficient solution under first order stochastic dominance and a hazard rate condition similar conditions allow full rent extraction in milgrom weber auctions

externalities in economies with imperfect information and incomplete markets this paper presents a simple general framework for analyzing externalities in economies with incomplete markets and imperfect infonnation by identifying the pecuniary effects of these externalities that net out the paper simplifies the problem of determining when tax interventions are pareto improving the approach indicates that such tax interventions almost always exist and that equilibria in situations of imperfect information are rarely constrained pareto optima it can also lead to simple tests based on readily observable indicators of the efficacy of particular tax policies in situations involving adverse selection signaling moral hazard incomplete contingent claims markets and queue rationing equilibria traditional discussions of externalities have emphasized the distinction between technological externalities in which the action of one individual or firm directly affects the utility or profit ofanother and pecuniary externalities in which one individual s or firm s actions affect another only through effects on prices while the presence of technological externalities imply in general that a competitive equilibrium may not be pareto efficient pecuniary externalities hy themselves are not a source of inefficiency the fact that prices change has of course important consequences there are both distributional and allocational effects but the distribution effects net out gains for example hy firms whose prices increase are precisely offset by losses e g to individuals who must pay higher prices and there are no welfare losses from the allocation effects as long as the price changes involved are small if firms are maximizing profits and individuals are maximizing utility both facing prices that correctly refiect opportunity costs then standard envelope theorem arguments imply that changes in profits or utility induced by changes in allocations resulting from any small change in prices are negligible

perfect competition in asymmetric information economies compatibility of efficiency and incentives the idea of perfect competition for an economy with asymmetric information is formalized via an idiosyncratic signal process in which the private signals of almost every individual agent can influence only a negligible group of agents and the individual agents relevant signals are essentially pairwise independent conditioned on the true states of nature thus there is no incentive for an individual agent to manipulate her private information the existence of incentive compatible ex post walrasian allocations is shown for such a perfectly competitive asymmetric information economy with or without common values consequently the conflict between incentive compatibility and pareto eciency is resolved exactly and its asymptotic version is derived for a sequence of large but finite private information economies

generic existence of completely revealing equilibria for economies with uncertainty when prices convey information conditions which imply the existence of strict rational expectations equilibria for most static pure exchange economies where prices convey information about the state of the world are analyzed information is aggregated and transmitted by prices because agents have different initial information and maximize the conditional expectation of state dependent utility functions major results state that if with probability one agents characteristics do not vary too much as the state of the world varies then generically there exist equilibrium price functions which reveal all initial information more precisely if the support of the image measure is contained in a compact c1 manifold satisfying some technical conditions which is of sufficiently low dimension relative to the number of commodities then existence of completely revealing equilibria is generic any economy satisfying these assumptions can be approximated by a sequence of economies which also obey these assumptions and have completely revealing equilibrium price functions slight perturbations do not destroy the existence property

phasing out of environmentally harmful subsidies consequences of the 2003 cap reform abstract subsidies linked to production have been classified as environmentally harmful by the oecd a core element of the eu 2003 common agricultural policy cap reform is to decouple income support from production this paper estimates the environmental consequences of this policy reform an agricultural sector model using a modified version of the positive mathematical programming method depicts the complex natural structural and political relationships of austrian farming changes in management measures can be analyzed with respect to their environmental effects by using appropriate indicators simulation results show that the 2003 cap reform will reduce the average cost of production and may improve environmental conditions regarding soil water and greenhouse gases when compared to a scenario without reform thus the new cap is likely to bring about outcomes which the previous reform agenda 2000 promised but did not deliver

equilibria and incentives in private information economies abstract this paper considers three solution concepts in a large private information economy namely walrasian expectations equilibrium private core and insurance equilibrium it shows that these three concepts coincide with each other when the agents are informationally negligible in such an economy in contrast to the finite agent setting one can construct a large private information economy in which incentive compatibility fails completely in the sense that almost every agent in any walrasian expectations equilibrium private core insurance equilibrium allocation has the incentive to misreport her type

the relevance of private information in mechanism design abstract recent results in mechanism design show that as long as agents have correlated private information and are sufficiently risk neutral it is possible to design mechanisms that leave agents with arbitrarily small information rents we show that these full rent extraction results hinge on the implicit assumption that the agents beliefs uniquely determine their preferences we present an example of the voluntary provision of a public good in which this assumption is relaxed and consequently even in highly correlated environments if agents beliefs do not uniquely determine their preferences then the extraction of the agents entire information rents is impossible

integrating agri environmental programs into regional production models an extension of positive mathematical programming positive mathematical programming pmp has become a popular method for regional production models the standard approach estimates cost or production functions for each land use activity separately from each other this means that the same crop grown under two technologies is treated as if it were two separate crops which may lead to unsatisfying results for example if agri environmental programs are modeled we present an extended version of pmp that leads to more plausible results than the standard version in such cases the extended method is applicable to other problems where differences in the elasticity of substitution between activities are important

informational size and incentive compatibility with aggregate uncertainty in mclean and postlewaite econometrica 56 1992 p 2421 we analyzed pure exchange economies with asymmetrically informed agents we defined a notion of informational size and showed that when the aggregate information of all agents resolves nearly all the uncertainty regarding the state of nature the conflict between incentive compatibility and ex post efficiency can be made small if agents have sufficiently small informational size this paper investigates the relationship between informational size and efficiency for the case in which nontrivial aggregate uncertainty is present i e when significant uncertainty about the world persists even when the information of all agents is known

asymmetric information bargaining problems with many agents a yes or no decision must be made about some issue all agents must agree the coase theorem asserts that the efficient outcome will always result suppose the value positive or negative that an individual attaches to an affirmative decision is privately known to that individual it is proved under very mild conditions that with independent types as the number of agents increases the probability of an affirmative efficient decision goes to zero an example in which it is common knowledge that an affirmative decision is efficient and yet the probability of such a decision goes to zero is given

information aggregation in a large multi stage market game abstract a three stage market game mechanism is devised that is simple actions are quantities and outcomes are determined by arithmetic operations that do not depend on details of the economy and achieves efficiency in a two divisible good pure exchange setting with potential information aggregation after an entry stage agents make offers which are provisional for all but a small randomly selected group then those offers are announced and everyone else makes new offers with payoffs determined by a shapley shubik market game for a finite and large number of players there exists an almost ex post efficient equilibrium conditions for uniqueness are also provided

core convergence with asymmetric information we analyze the ex ante incentive compatible core for replicated private information economies we show that any allocation in the core when the economy is replicated sufficiently often is approximately walrasian for the associated arrow debreu economy

primal dual positive math programming illustrated through an evaluation of the impacts of market resistance to genetically modified grains the goal of howitt s positive mathematical programming procedure is to calibrate a mathematical programming model so that it will reproduce a set of base data for the primal variables this article develops an analogous procedure allowing one to specify the levels of both primal and dual variables this article also sheds light on a potential ambiguity of howitt s procedure with attendant policy evaluation impacts the procedure is illustrated through application to an equilibrium displacement model focused on evaluating the consequences of the reluctance of u s trading partners to accept genetically modified crop products for u s production patterns and net farm income copyright 2002 oxford university press

implementation of walrasian expectations equilibria in an exchange economy with differentially informed traders non exclusivity of information nei is the condition that each trader s private information be perfectly predictable by an outside observer who has observed the private information of all other traders nei is one of a set of conditions which taken together are sufficient for the implementability of fully revealing expectations equilibria here we show that this condition is in fact necessary for the weak implementation of a much broader class of walrasian equilibria herein called expectations equilibria

full extraction of the surplus in bayesian and dominant strategy auctions we consider auctions for a single indivisible object in the case where the bidders have information about each other which is not available to the seller we show that the seller can use this information to his own benefit and we completely characterize the environ ments in which a well chosen auction gives him the same expected payoff as that obtainable were he able to sell the object with full information about each bidder s willingness to pay we provide this characterization for auctions in which the bidders have dominant strate gies and for those where the relevant equilibrium concept is bayesian nash in both set ups the existence of these auctions hinges on the possibility of constructing lotteries with the correct properties we consider the situation in which an agent the seller possesses one indivisible unit of a good to which he attaches no value but the good has value to a number of potential buyers and its transfer to one of them would increase social welfare in particular the transfer to the buyer with the highest valuation maximizes social welfare in this paper we completely characterize environments in which the seller can design an auction that will enable him to capture for himself the full increase in social welfare induced by the transfer of the good to the bidder with the highest willingness to pay if the seller had full information about the reservation prices of potential buyers his optimal selling strategy would be very simple he would announce a price equal or very close to the highest reservation value the optimal strategy for the bidder with the highest evaluation would be to accept the offer note that we are treating a situation in which the seller can commit himself to a price as a result of the exchange the utility of the seller increases by the full amount of the increase in social welfare and he has been able to fully extract the surplus in many circumstances however a seller has only imperfect knowledge of the buyers willingnesses to pay in this case he must find some mechanism or auction which will enable him to maximize his benefit from the sale of the object the auction literature starts with this observation and shows how the seller can by an astute choice of auction extract the largest possible fraction of the surplus in general the literature has shown that this proportion is strictly less than one in some circumstances the bidders will have information about each other which is not available to the seller for instance in auctions for petroleum drilling rights bidders know the results of geological tests which they have

informational size and incentive compatibility we examine a general equilibrium model with asymmetrically informed agents the presence of asymmetric information generally presents a conflict between incentive com patibility and pareto efficiency we present a notion of informational size and show that the conflict between incentive compatibility and efficiency can be made arbitrarily small if agents are of sufficiently small informational size the incompatibility of pareto efficiency and incentive compatibility is a central theme in economics and game theory the issues associated with this incompatibility are particularly important in the design of resource allocation mechanisms in the presence of asymmetrically informed agents where the need to acquire information from agents in order to compute efficient outcomes and the incentives agents have to misrepresent that information for personal gain come into conflict despite a large literature that focuses on these issues there has been little work aimed at understanding those situations in which informational asymmetries are quantitatively important virtually every transaction is characterized by some asymmetry of information any investor who buys or sells a share of stock generally knows something rel evant to the value of the share that is not known to the person on the other side of the transaction in order to focus on more salient aspects of the problem many models rightly ignore the incentive problems associated with informa tional asymmetries in the belief that for the problem at hand agents are infor mationally small however few researchers have investigated the circumstances under which an analysis that ignores these incentive problems will yield results similar to those obtained when these problems are fully accounted for in this paper we study a class of mechanism design problems our goal is to formalize informational size in a way that when agents are informationally small 1 early versions of this paper circulated under the titles informational smallness and pareto effi ciency and informational smallness and incentive compatibility we thank jacques cremer dean foster andreu mas colell stephen morris david schmeidler and particularly faruk gul for help ful conversations and rajiv vohra for a very careful reading we also thank the numerous partici pants in seminars at which this paper was presented for helpful comments we also thank an editor and the referees for very helpful comments and thank ichiro obara for pointing out an error in an earlier version postlewaite gratefully acknowledges support from the national science foundation

a competitive distribution of auctions in this paper a competitive distribution of auctions is described for an economy consisting of an infinite number of buyers and sellers all of whom differ according to their valuation for the single indivisible object being traded a competitive distribution of auctions is such that no seller can improve his profits by deviating to any alternative direct mechanism it is shown that the competitive distribution of auctions will have the property that each buyer and seller s best reply is independent of his beliefs about the tastes of other buyers and sellers on the market the purpose of this paper is to provide an equilibrium for an economy in which sellers compete by offering different direct mechanisms to buyers no attempt is made to give a complete characterization of all possible equilibria rather we focus on one equilibrium in which the contracts that are offered by sellers in equilibrium and buyer s behaviour under these contracts are both independent of traders beliefs about one another the equilibrium illustrates one of the reasons why contracts that are employed in practice may not be as finely tuned to beliefs as the theory of mechanism design says that they should be the answer is simply that contracts are not offered in a vacuum sellers in the model studied in this paper need to compete with one another in order to attract buyers highly tuned mechanisms tend to extract buyer surplus in such an environment sellers are able to attract many buyers by offering to use cruder mechanisms that leave some surplus for buyers in this paper sellers are allowed to have different costs for the commodity that is being traded nonetheless the equilibrium for the limit economy in which there are infinitely many buyers and sellers is such that every seller offers a second price auction and publicizes a reserve price equal to his cost in a standard monopoly auction the optimal reserve price for the seller exceeds his cost by an amount that depends on his beliefs about buyers valuations myerson 1981 a seller who raises his reserve price has his profits affected in two distinct ways by raising his reserve price the seller makes it unprofitable for some buyer types to participate in his auction the seller therefore loses any surplus that he might have earned by trading with these buyers the buyers who still find it profitable to participate in the seller s auction will end up having to pay a higher price when they win because of this increase in the seller s reserve price this means that the seller will be able to extract a bit more surplus from buyers who continue to participate the seller raises the reserve price until the marginal cost associated with raising the reserve price is just equal to the marginal gain associated with the ability to extract more surplus from remaining buyers competition mitigates this argument since there is a limit to the amount of surplus that the seller can extract from remaining buyers before they decide that they should instead choose one of the alternative auctions that are being held on the market with

informational robustness of competitive equilibria abstract consider an exchange economy with complete information we perturb this economy by assuming that each agent s observation about the true state of the world is noisy the paper investigates the robustness of equilibria of the complete information economy with respect to incomplete information we provide conditions under which complete information equilibria are limits of equilibria of the economies with incomplete information as the noise in the signal converges to zero journal of economic literature classification numbers d51 d82

the rate at which a simple market converges to efficiency as the number of traders increases an asymptotic result for optimal trading mechanisms private information in an independent private values market provides incentives to traders to manipulate equilibrium prices strategically this strategic behavior precludes ex post efficient market performance increasing the number of traders improves the efficiency of some trading mechanisms by enabling them to better utilize the private information traders bids and offers reveal this paper shows that the expected inefficiency of optimally designed mechanisms relative to ex post efficient allocations decreases almost quadratically as the number of traders increases