Strong comparative statics of equilibria

Some results in the monotone comparative statics literature tell us that if a parameter increases, some old equilibria are smaller than some new equilibria. We give a sufficient condition such that at a new parameter value every old equilibrium is smaller than every new equilibrium. We also adapt a standard algorithm to compute a minimal such newer parameter value and apply this algorithm to a game of network externalities. Our results are independent of a theory of equilibrium selection and are valid for games of strategic complementarities.     

A characterization of strategic complementarities

I characterize games for which there is an order on strategies such that the game has strategic complementarities. I prove that, with some qualifications, games with a unique equilibrium have complementarities if and only if Cournot best-response dynamics has no cycles; and that all games with multiple equilibria have complementarities. As applications of my results, I show that: (1) generic 2×2 games either have no pure-strategy equilibria, or have complementarities; (2) generic two-player finite ordinal potential games have complementarities.     

Uncertainty, co-ordination and path dependence

Our objective is to assess whether dynamics hinder or assist co-ordination in a game with strategic complementarities. We study two dynamic aspects: different agents make decisions at different points in time; and extra information about a payoff-relevant state of nature becomes available over time. We find that the dynamic resolution of information matters most for uniqueness of equilibrium. This is demonstrated by showing that the condition for uniqueness is weaker when learning occurs. We also analyse how successfully agents co-ordinate when there is a unique equilibrium. Finally, we show that path dependence occurs: the order in which signals arrive matters, as well as the total amount of information received.     

GLOBAL GAMES WITH STRATEGIC SUBSTITUTES

We study global games with strategic substitutes. Specifically, for a class of binary‐action, ‐player games with strategic substitutes, we prove that under payoff asymmetry, as incomplete information vanishes, the global games approach selects a unique equilibrium. We characterize this equilibrium profile ; players employ switching strategies at different cutoff signals, the order of which is directly determined by payoff asymmetry. We provide examples that illustrate our result and its connection with dominance solvability. We extend the global game literature, which has thus far been developed for games with strategic complementarities, to new applications in industrial organization, collective action problems, finance, etc .     

A note on Stackelberg competition

This note investigates a Stackelberg–Nash competition model. We determine the conditions under which the leaders may achieve better profits than the followers when all firms compete on quantity in a two stage game. We focus on the properties of the followers’ best response functions. It is shown that the Stackelberg equilibrium may coincide with the Cournot equilibrium. In addition, the followers may achieve higher profits than the leaders. Such results put forward the working and the consequences of strategic complementarities. These results are illustrated with three examples.     

A unified approach to comparative statics puzzles in experiments

The paper shows that several game-theoretic solution concepts provide similar comparative statics predictions over a wide class of games. I start from the observation that, in many experiments, behavior is affected by parameter shifts that leave the Nash equilibrium unchanged. I explain the direction of change with a heuristic structural approach, using properties such as strategic complementarities and increasing differences. I show that the approach is consistent with general comparative statics results for (i) the Nash equilibrium of a game with perturbed payoff functions, (ii) the quantal response equilibrium, (iii) level-k reasoning. I also relate the structural approach to equilibrium selection concepts.     

Characterising equilibrium selection in global games with strategic complementarities

Global games are widely used to predict behaviour in games with strategic complementarities and multiple equilibria. We establish two results on the global game selection. First, we show that, for any supermodular complete information game, the global game selection is independent of the payoff functions chosen for the game?s global game embedding. Second, we give a simple sufficient criterion to derive the selection and establish noise independence in many-action games by decomposing them into games with smaller action sets, to which we may often apply simple criteria. We also report in which small games noise independence may be established by counting the number of players or actions.     

Measuring Strategic Uncertainty in Coordination Games

This paper proposes a method to measure strategic uncertainty by eliciting certainty equivalents analogous to measuring risk attitudes in lotteries. We apply this method by conducting experiments on a class of one-shot coordination games with strategic complementarities and choices between simple lotteries and sure payoff alternatives, both framed in a similar way. Despite the multiplicity of equilibria in the coordination games, aggregate behaviour is fairly predictable. The pure or mixed Nash equilibria cannot describe subjects' behaviour. We present two global games with private information about monetary payoffs and about risk aversion. While previous literature treats the parameters of a global game as given, we estimate them and show that both models describe observed behaviour well. The global-game selection for vanishing noise of private signals offers a good recommendation for actual players, given the observed distribution of actions. We also deduce subjective beliefs and compare them with objective probabilities.     

Decompositions and potentials for normal form games

A basic model of commitment is to convert a two-player game in strategic form to a “leadership game” with the same payoffs, where one player, the leader, commits to a strategy, to which the second player always chooses a best reply. This paper studies such leadership games for games with convex strategy sets. We apply them to mixed extensions of finite games, which we analyze completely, including nongeneric games. The main result is that leadership is advantageous in the sense that, as a set, the leader's payoffs in equilibrium are at least as high as his Nash and correlated equilibrium payoffs in the simultaneous game. We also consider leadership games with three or more players, where most conclusions no longer hold.     

Asynchronized multiperiod commitments and cycles

We consider a game where agents can synchronize or stagger their decisions. We compare the outcomes of both timing patterns, and show that spillovers and strategic interactions are crucial for such a comparison. A typology used in industrial organization, distinguishing four cases (‘Fat-Cat’, ‘Top Dog’, Lean and Hungry’, ‘Puppy Dog’), allows us to compare the actions taken in the staggered variant and in the synchronized one. The staggered variant exhibits cycles and players are both better-off when there are strategic complementarities between them. A timing game is then set-up so as to endogenize the choice between the two variants we study.Two examples are developed: (i) Bertrand competition and (ii) a wage setting game when there are two monopoly unions in two interrelated firms. We show that the staggering of price decisions generates counter-cyclical mark-ups in the first example, and the staggering of wage decisions generates cycling output in the industry in the second example.     

Path Dependence and Learning from Neighbors

We study the long-run properties of a class of locally interactive learning systems. A finite set of players at fixed locations play a two-by-two symmetric normal form game with strategic complementarities, with one of their “neighbors” selected at random. Because of the endogenous nature of experimentation, or “noise,” the systems we study exhibit a high degree of path dependence. Different actions of a pure coordination game may survive in the long-run at different locations of the system. A reinterpretation of our results shows that the local nature of search may be a robust reason for price dispersion in a search model,Journal of Economic LiteratureClassification Numbers: C72, D83.     

Monotone equilibria in Bayesian games of strategic complementarities

For Bayesian games of strategic complementarities, we provide a constructive proof of the existence of a greatest and a least Bayesian Nash equilibrium, each one in strategies that are monotone in type. Our main assumptions, besides strategic complementarities, are that each player's payoff displays increasing differences in own action and the profile of types and that each player's interim beliefs are increasing in type with respect to first-order stochastic dominance (e.g., types are affiliated). The result holds for general action and type spaces (single-, multi-, or infinite-dimensional; continuous or discrete) and no prior is assumed. We also provide the following comparative statics result: the greatest and least equilibria are higher if there is a first-order stochastic dominant shift in the interim beliefs. We apply this result to strategic information revelation in games of voluntary disclosure.     

Strategic Consumption Complementarities: Can Price Flexibility Eliminate Inefficiencies and Instability?

Generally, two facts occur with strategic complementarities and fixed prices: (i) the equilibria are multiple and (ii) if the complementarities are strong, the law of demand is violated and the equilibrium is unstable. In this paper, we analyse the effect of price flexibility on these features as well as on market welfare properties. Assuming an exchange economy with H agents consuming two goods with one strategic complement, we show that flexibility of prices may remove both the multiplicity of the equilibria and the instability of behavior when the externalities are strong. Moreover, we find conditions to correct instability when it is caused by perverse wealth effects. When preferences are quasilinear and identical, if the externality is beneficial, any equilibrium is Pareto optimal despite the externality. But if the externality is detrimental, corrections are required.     

Implementations of the Nash solution based on its Walrasian characterization

Summary. The present paper provides three different support results for the Nash bargaining solution of -person bargaining games. First, for any bargaining game there is defined a non-cooperative game in strategic form, whose unique Nash equilibrium induces a payoff vector that coincides with the Nash solution of the bargaining game. Next this game is modified in such a way that the unique Nash equilibrium that supports the Nash solution is even in dominant strategies. After that an -stage game in extensive form is presented whose unique subgame perfect equilibrium supports the Nash solution of the bargaining game. Finally, the support results are shown to induce implementation results in the sense of mechanism theory. Received: October 3, 1999; revised version: October 26, 1999     

Learning in games with strategic complementarities revisited

Fictitious play is a classical learning process for games, and games with strategic complementarities are an important class including many economic applications. Knowledge about convergence properties of fictitious play in this class of games is scarce, however. Beyond games with a unique equilibrium, global convergence has only been claimed for games with diminishing returns [V. Krishna, Learning in games with strategic complementarities, HBS Working Paper 92-073, Harvard University, 1992]. This result remained unpublished, and it relies on a specific tie-breaking rule. Here we prove an extension of it by showing that the ordinal version of strategic complementarities suffices. The proof does not rely on tie-breaking rules and provides some intuition for the result.     

Cooperation in Experimental Games of Strategic Complements and Substitutes

We conduct a laboratory experiment aimed at examining whether strategic substitutability and strategic complementarity have an impact on the tendency to cooperate in finitely repeated two-player games with a Pareto-inefficient Nash equilibrium. We find that there is significantly more cooperation when actions exhibit strategic complementarities than in the case of strategic substitutes. The difference is to some extent driven by a difference in the speed with which some pairs reach stable full cooperation, but mainly by differences in choices of pairs that do not succeed in reaching full cooperation.     

Endogenous Timing in Strategic Environmental Policymaking

In this paper, we endogenize the timing of policymaking in a simple two-country model of strategic environmental policy. We consider a timing game in which two policymakers non-cooperatively decide their preferred sequence of moves before setting emission tax rates. We show that whether the policymakers implement emission tax policies simultaneously or sequentially crucially depends on the magnitude of environmental damages. When the damages are insignificant, the tax rates are strategic substitutes, and the simultaneous-move policymaking emerges in equilibrium. In contrast, when the damages are significant, the tax rates are strategic complements, and sequential-move policymaking emerges. We also extend the model by allowing for differences in the vulnerability to environmental damages between countries. When the differences are large, the unique equilibrium of the game is the situation where the less vulnerable country acts as a leader. In the case where multiple equilibrium emerges, the risk-dominant equilibrium is also that where the less vulnerable country leads.     

Coordination and learning in games with strategic substitutes and complements

This paper experimentally compares the impact of the presence of strategic substitutes (GSS) and complements (GSC) on players’ ability to successfully play equilibrium strategies. By exploiting a simple property of the ordering on strategy spaces, our design allows us to isolate these effects by avoiding other confounding factors that are present in more complex settings, such as market games. We find that the presence of strategic complementarities significantly improves the rate of Nash play, but that this effect is driven mainly by early rounds of play. This suggests that GSS may be more difficult to learn initially, but that given sufficient time, the theoretically supported globally stable equilibrium offers a good prediction in both settings. We also show that increasing the degree of substitutability or complementarity does not significantly improve the rate of Nash play in either setting, which builds on the findings of previous studies.     

Endogenous Alleviation of Overreaction Problem by Aggregate Information Announcement

It is well‐known that agents overreact to public information in markets characterized by strategic complementarities. We propose a simple and implementable method of alleviating the overreaction problem. Extending the beauty‐contest game of Morris and Shin to a multi‐region economy, we show that, under an aggregate information announcement, each agent converts purely public information into imperfect public information endogenously. This makes the agents’ beliefs dispersed and alleviates the overreaction problem. Moreover, we compare the welfare effect of the aggregate information announcement with that of a separate announcement. We find that there exist plausible situations where the aggregate information announcement is better than the separate information announcement despite reduced quality.     

A note on network formation with decay

This paper studies an endogenous network formation with decay. We introduce a strategic form game based on a simple bilateral cost allocation rule. We show that a strong Nash equilibrium of this game always exists and necessarily achieves efficient networks.