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

nash implementation a complete characterization the authors extend e maskin s results on nash implementation first they establish a condition that is both necessary and sufficient for nash implementability if there are three or more agents the case covered by maskin s sufficiency result second and more important they examine the two agent case for which there existed no general sufficiency results the two agent model is the leading case for applications to contracting and bargaining for this case too they establish a condition that is both necessary and sufficient the authors use their theorems to derive simpler sufficiency conditions that are applicable in a wide variety of economic environments copyright 1990 by the econometric society

exit options in incomplete contracts with asymmetric information this paper analyzes bilateral contracting in an environment with contractual incompleteness and asymmetric information one party the seller makes an unverifiable quality choice and the other party the buyer has private information about its valuation a simple exit option contract which allows the buyer to refuse trade achieves the first best in the benchmark cases where either quality is verifiable or the buyer s valuation is public information but when unverifiable and asymmetric information are combined exit options induce inefficient pooling and lead to a particularly simplecontract inefficient pooling is unavoidable also under the most general form of contracts which make trade conditional on the exchange of messages between the parties indeed simple exit option contracts are optimal if random mechanisms are ruled out

deviations from purchasing power parity in the long run this paper demonstrates that deviations from purchasing power parity reveal a remarkable and possibly startling consistency with martingale behavior during both fixed and flexible rate periods for a wide variety of countries and in both monthly and annual data since this pattern appears to be much more general than one would expect on the basis of models founded on international commodity arbitrage the paper proposes an alternative explanation which instead relies on financial arbitrage in bonds as the underlying mechanism this paper will demonstrate that deviations from purchasing power parity ppp reveal a remarkable and possibly startling consistency with martingale behavior during both fixed and flexible exchange rate periods for a wide variety of countries and in both monthly and annual data this pattern appears to be much more general than one would expect on the basis of models founded on international commodity arbitrage the paper therefore proposes an alternative explanation which does not presuppose free trade in goods but which instead relies on financial arbitrage in bonds as the underlying mechanism the major implication of the theory and the results is that ppp is as likely to be violated in the long as in the short run as an empirical matter deviations from ppp can be observed for most currencies at any instant see kravis et al 21 stockman 37 and genberg 15 among others these deviations are typically both cumulative and persistent the real exchange rate can remain on either side of parity for lengthy but variable time intervals of a year or more as a consequence the current consensus shared

two remarks on the property rights literature we first point out that the recent property rights literature is based on three assumptions 1 that contracts are always subject to renegotiation 2 that the exercise of a property right confers a private benefit and 3 that parties are risk neutral building on hart moore 1999 we provide conditions under which an optimal contract consists of nothing more than an assignment of property rights we also examine the robustness of some of the literature s standard predictions about asset ownership to the introduction of mechanisms for eliciting parties ex post willingness to pay for the assets such as options or financial markets to illustrate the issue we revisit the hart moore 1990 proposition that joint ownership is suboptimal and argue that ownership by a single party is dominated by joint ownership with put options

simple mechanisms and preferences for honesty we consider full implementation in complete information environments when agents have an arbitrarily small preference for honesty we offer a condition called separable punishment and show that when it holds and there are at least two agents any social choice function can be implemented by a simple mechanism in two rounds of iterated deletion of strictly dominated strategies

unforeseen contingencies and incomplete contracts we scrutinize the conceptual framework commonly used in the incomplete contract literature this literature usually assumes that contractual incompleteness is due to the transaction costs of describing or of even foreseeing the possible states of nature in advance we argue however that such transaction costs need not interfere with optimal contracting i e transaction costs need not be relevant provided that agents can probabilistically forecast their possible future payoffs even if other aspects of the state of the nature cannot be forecast in other words all that is required for optimality is that agents be able to perform dynamic programming an assumption always invoked by the incomplete contract literature the foregoing optimality result holds very generally provided that parties can commit themselves not to renegotiate moreover we point out that renegotiation may be hard to reconcile with a framework that otherwise presumes perfect rationality however even if renegotiation is allowed the result still remains valid provided that parties are risk averse

the tradeoff of the commons under stochastic use abstract we develop a model of scarce renewable resources to study the problem of the commons our model formulation differs from the existing literature in that it assumes the use of the commons to be stochastic in nature one example is microwave spectrum for mobile and wireless communications we investigate three mechanisms of resource allocation free usage the exclusive franchise and a regulated monopoly we show that the welfare tradeoff among these three mechanisms depends on the characteristics of the commons and their usage patterns in particular we find that property rights are not always the best solution we then make four extensions that apply to spectrum allocations

the role of bounded rationality and imperfect information in subgame perfect implementation an empirical investigation in this paper we conduct a laboratory experiment to test the extent to which moore and repullo s subgame perfect implementation mechanism induces truth telling in practice both in a setting with perfect information and in a setting where buyers and sellers face a small amount of uncertainty regarding the good s value we nd that moore repullo mechanisms fail to implement truth telling in a substantial number of cases even under perfect information about the valuation of the good this failure to implement truthtelling is due to beliefs about the irrationality of one s trading partner therefore although the mechanism should in theory provide incentives for truth telling many buyers in fact believe that they can increase their expected monetary payo by lying the deviations from truth telling become signicantly more frequent and more persistent when agents face small amounts of uncertainty regarding the good s value our results thus suggest that both beliefs about irrational play and small amounts of uncertainty about valuations may constitute important reasons for the absence of moore repullo mechanisms in practice

spectrum auctions yesterday s heresy today s orthodoxy tomorrow s anachronism taking the next step to open spectrum access abstract the auction paradigm for spectrum allocation has moved from heresy to orthodoxy but like its predecessors it will not be the end of history a better alternative not driven by the revenue needs of government is license free spectrum users would gain entry to frequency bands on a pay as you go basis instead of controlling a slice of the spectrum they would transmit their content together with access tokens these tokens are electronic money access prices would vary with congestion set by automatic clearinghouses of spectrum users spot and futures markets for spectrum access would emerge once technology and economics can solve the interference problem in ways other than exclusivity the question arises whether the right to use the spectrum for electronic speech is the government s to sell in the first place

testing for long run purchasing power parity a time series analysis for the greek drachma abstract long run purchasing power parity ppp for six drachma bilateral exchange rates is tested by means of unit root and cointegration tests the results reject long run ppp

incomplete contracts and the theory of the firm what have we learned over the past 25 years incomplete contracts and the theory of the firm what have we learned over the past 25 years

the long run relationship between the real exchange rate and terms of trade in oecd countries using the null hypothesis of cointegration it is shown that the real exchange rate and the terms of trade of the seven major oecd countries are cointegrated in the long run our results also confirm the granger proposition that there is granger causality in at least one direction when two variables are i 1 and cointegrated we find that exchange rate changes granger cause changes in the terms of trade for five out of the seven oecd countries while the causation runs in the opposite direction for the remaining two countries

the tradeoff of the commons we develop a model of scarce renewable resources to study the commons problem we show that contrary to conventional wisdom property rights can often be less efficient than a commons in particular we study two effects 1 waste which arises when individuals expend resources to use a resource unavailable due to congestion and 2 the risk of underutilization of the resource we provide necessary and sufficient conditions for each effect to dominate the other when the cost of determining the availability of a resource is low

efficiency despite mutually payoff relevant private information the finite case individuals have or observe partly private information they independently choose acts possibly including messages the center may also act individuals utilities may depend on all acts and information including others private information are there incentives depending only on public information that make desired behavior a bayesian equilibrium assume incentive payments are separable and fully transferable appropriate incentives exisit either if the center s information depends stochastically however slightly on all relevant private information or if individuals relative valuations of acts however divergent are not too dissimilarly affected by different states of nature more generally one gives necessary and sufficient conditions for existence whenever the strategy profile asks agents to reveal all private knowledge relevant to their beliefs about the center s information

cooperative investments and the value of contracting recent articles have shown that contracts can support the efficient outcome for bilateral trade even in the face of specific investments and incomplete contracting these studies typically considered selfish investments that benefit the investor e g the seller s investment reduces her production costs the authors find very different results for cooperative investments that directly benefit the investor s partner e g the seller s investment improves the buyer s value of the good most importantly if committing not to renegotiate the contract is impossible then contracting has no value i e the parties cannot do better than to abandon contracting altogether in favor of ex post negotiation

contributions of oliver hart and bengt holmstrom to contract theory oliver hart and bengt holmstrom were awarded the 2016 sveriges riksbank prize in economic sciences in memory of alfred nobel for their fundamental contributions to contract theory this article offers a short summary and discussion of their path breaking work

efficient investments in the implementation problem abstract this paper identifies a condition for an efficient social choice rule to be fully implementable when we take into account investment efficiency to do so we extend the standard implementation problem to include endogenous ex ante and ex post investments in our problem the social planner aims to achieve efficiency in every equilibrium of a dynamic game in which agents strategically make investments before and after playing the mechanism our main theorem shows that a novel condition commitment proofness is sufficient and necessary for an efficient social choice rule to be implementable in subgame perfect equilibria the availability of ex post investments is crucial in our model there is no social choice rule that is efficient and implementable in subgame perfect equilibria without ex post investments we also show that our positive result continues to hold in the incomplete information setting

spectrum flash dance eli noam s proposal for open access to radio waves abstract as ronald coase posited in his famous article on the nature of the firm there are situations in which decentralized markets are relatively efficient for coordinating economic activity and situations in which they are not with spectrum access assigning property rights to clearly specified private owners is the socially efficient policy because the relevant transaction efficiencies will be internalized by competitive spectrum owners selecting to what degree rights should be subdivided and in what manner marketed where spot markets are optimal an owner will maximize profits by using them where long term contracts are efficient the owner will enter profitably into them hence eli noam s solution imposing open access rules on bands of radio frequencies by government mandate is a mistaken attempt to duplicate the efficiencies of markets by mandating a particular subset of market solutions such a policy predictably will result in underutilization of the spectrum resource

the spectrum as commons tomorrow s vision not today s prescription abstract eli noam has proposed using nascent technologies to treat the electromagnetic spectrum as an open access commons rather than as a subdivided collection of property rights in his view public auctions reduce competition threaten free speech foster fiscal mismanagement and presume illegitimate government ownership of spectrum but government auctioning is our collective decision to sell that which we all own to foster spectrum efficiency via the market threats to free speech are exaggerated especially when asserted on behalf of corporations noam correctly observes that a government auctioneer might make too little spectrum available but concerns about fostering oligopoly are exaggerated his open access alternative would likely increase the cost of assembling the substantial long term rights to use spectrum for standardized reliable telecommunication services if the benefits of open access ever exceed the costs spectrum owners could carry out the necessary subdivision management and

subgame perfect implementation this paper examines the use of stage mechanisms in implementation problems and provides a partial characterization of the set of subgam e perfect implementable choice rules it is shown that in many economic environments virtually an y choice rule can be implemented to illustrate the power of this approach the paper discusses a number of models in which it is possible to implement the first best although it wouldn t have been possible to do so without using stage mechanisms the diversity of these models suggests that subgame perfect implementation may find wide application copyright 1988 by the econometric society

subgame perfect implementation under information perturbations we consider the robustness of extensive form mechanisms to deviations from common knowledge about the state of nature which we refer to as information perturbations first we show that even under arbitrarily small information perturbations the moore repullo mechanism does not yield even approximately truthful revelation and that in addition the mechanism has sequential equilibria with undesirable outcomes more generally we prove that any extensive form mechanism is fragile in the sense that if a non maskin monotonic social objective can be implemented with this mechanism then there are arbitrarily small information perturbations under which an undesirable sequential equilibrium also exists finally we argue that outside options can help improve efficiency in asymmetric information environments and that these options can be thought of as reflecting ownership of an asset

rational behavior with payoff uncertainty abstract the iterated deletion of weakly dominated strategies has been advanced as a necessary requirement for rational play however this requirement relies on the assumption that the players have no doubts about their opponents payoffs we show that once such doubts are introduced all that can be justified by an appeal to rationality is one round of deletion of weakly dominated strategies followed by iterated deletion of strategies that are strongly dominated this extends the fudenberg kreps and levine j econ theory 12 1988 354 380 study of the robustness of nash equilibrium refinements to the robustness of solution concepts based only on rationality our results also clarify the relationship between various notions of what it means for payoff uncertainty to be small

purchasing power parity abstract this paper examines the purchasing power parity henceforth ppp using historical data and the cointegration approach the results indicate that the exchange rate is cointegrated with the wholesale price index wpi ratio but not with the consumer price index cpi ratio the cointegrating vector is close to 0 1 for the cpi based real exchange rates however we cannot reject the random walk hypothesis the findings caution us on the use of general price indexes that give a large weight to nontraded goods and are therefore subject to long run deviations from ppp

terms of trade and the exchange rates of new zealand and australia effects of the terms of trade on the bilateral exchange rate of new zealand and australia and of each of these countries with the usa are evaluated there is strong evidence of cointegration of the exchange rates and a ration of the respective national price levels when the relative terms of trade of the countries are included in dynamic models while evidence that the long run equilibrium relationships satisfy purchasing power parity is mixed relative improvement of a country s terms of trade results in real appreciation of its currency in all cases the terms of trade are also found to be exogenous for the parameters of the long run new zealand australia exchange rate equilibrium

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

nash equilibrium and welfare optimality if is a set of social alternatives a social choice rule scr assigns a subset of a to each potential profile of individuals preferences over a where the subset is interpreted as the set of welfare optima a game form or mechanism implements the social choice rule if for any potential profile of preferences 1 any welfare optimum can arise as a nash equilibrium of the game form implying in particular that a nash equilibrium exists and 2 all nash equilibria are welfare optimal the main result of this paper establishes that any scr that satisfies two properties monotonicity and no veto power can be implemented by a game form if there are three or more individuals the proof is constructive

optimal abolition of fcc spectrum allocation ronald coase based his 1959 call for spectrum markets on theoretical conjecture today abundant evidence supports his case targeted liberalization in cellular markets as contrasted with regulatory planning of the digital tv transition and other traditional policies suggest enormous efficiency gains are available from wider use of the price system with exclusive frequency rights assigned to owners markets widely reconfigure spectrum use coordinating complex spectrum sharing resulting social gains include increased consumer surplus from enhanced technological innovation and wireless service competition a social bonus arrives in the benefits associated with wider scope for free speech yet the administrative allocation system continues to distribute rents and garner political support liberal reforms in contrast produce large but broadly dispersed efficiency gains and are undersupplied this paper proposes an incremental extension of property rights in spectrum to move beyond the current rent seeking equilibrium eliminating the federal communications commission s centralized spectrum allocation process and with it an attractive nuisance generating anticonsumer outcomes