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.     

Optimal Fiscal Policy with Endogenous Time Preference

This paper studies the role of Ramsey taxation under the assumption that the individual rate of time preference is determined by the publicly provided social level of education. We show how intertemporal complementarities of aggregate human capital can generate multiple equilibria and we examine the role of endogenous fiscal policies in equilibrium selection. Our analysis implies a lower optimal government size due to the effect of human capital on time preference.     

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.     

Complementarities between firm-sponsored training and information technology use

In this article, we investigate the presence of possible complementarities between investments in information technology (IT) and firm-sponsored training using economy-wide longitudinal representative workplace-level data. Since information on the firm’s capital stock is often missing in such representative data, we match our workplace records to tax data to construct measures of the firm’s capital stock. We find some evidence of positive complementarities between investments in human capital and IT, suggesting that on-the-job training can also have a positive impact on productivity when complemented with investments in CAD or other technologies.     

Opportunist politicians and the evolution of electoral competition

This paper studies a uni-dimensional model of electoral competition between two parties with two types of politicians. ‘Opportunist’ ones care only about the spoils of the office, and ‘militant’ ones have ideological preferences on the policy space. Opportunist politicians review their affiliations and may switch parties, seeking better election prospects. In this framework, we compare a winner-take-all system, where all the spoils of office go to the winner, to a proportional system, where the spoils of office are split among the two parties in proportion to their vote shares. We study the existence of short term political equilibria and the dynamics and stability of policies and of party membership decisions. In the long run, it is possible that proportional systems see opportunist politicians spread over all parties, but this situation is unstable in winner-take-all systems.     

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.     

Rebate rules in threshold public good provision

This paper considers how six alternative rebate rules affect voluntary contributions in a threshold public-good experiment. The rules differ by (1) whether an individual can receive a proportional rebate of excess contributions, a winner-takes-all of any excess contributions, or a full rebate of one's contribution in the event the public good is provided and excess contributions exist, and (2) whether the probability of receiving a rebate is proportional to an individual's contribution relative to total contributions or is a simple uniform probability distribution set by the number of contributors. The paper adds to the existing experimental economics literature on threshold public goods by investigating both aggregate and individual demand revelation under the winner-take-all and random full-rebate rules. Half of the rules (proportional rebate, winner-take-all with uniform probability among all group members, and random full-rebate with uniform probability) provide total contributions that nearly equal total benefits, while the rest (winner-take-all with proportional probability, winner-take-all with uniform probability among contributors only, and random full-rebate with proportional probability) exceed benefits by over 30%. Only the proportional rebate rule is found to achieve both aggregate and individual demand revelation. Our experimental results have implications for both fundraisers and valuation practitioners.     

POLITICS WITH AND WITHOUT POLICY†

When strategic complementarities lead to the existence of multiple equilibria, a change in control of government may lead to changes in economic behavior by consumers or firms even if the different parties pursue the same policies. The existence of multiple equilibria, however, is not necessary to predict partisan effects. Furthermore, electoral uncertainty is not necessary to generate partisan effects; indeed, such uncertainty can dampen the cycle.     

Mixed equilibria in games of strategic complementarities

Summary. The literature on games of strategic complementarities (GSC) has focused on pure strategies. I introduce mixed strategies and show that, when strategy spaces are one-dimensional, the complementarities framework extends to mixed strategies ordered by first-order stochastic dominance. In particular, the mixed extension of a GSC is a GSC, the full set of equilibria is a complete lattice and the extremal equilibria (smallest and largest) are in pure strategies. The framework does not extend when strategy spaces are multi-dimensional. I also update learning results for GSC using stochastic fictitious play. Received: October 16, 2000; revised version: March 7, 2002 RID="*" ID="*" I am very grateful to Robert Anderson, David Blackwell, Aaron Edlin, Peter De Marzo, Ted O'Donoghue, Matthew Rabin, Ilya Segal, Chris Shannon, Clara Wang and Federico Weinschelbaum for comments and advise.     

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.     

Learning to alternate

The Individual Evolutionary Learning (IEL) model explains human subjects’ behavior in a wide range of repeated games which have unique Nash equilibria. Using a variation of ‘better response’ strategies, IEL agents quickly learn to play Nash equilibrium strategies and their dynamic behavior is like that of humans subjects. In this paper we study whether IEL can also explain behavior in games with gains from coordination. We focus on the simplest such game: the 2 person repeated Battle of Sexes game. In laboratory experiments, two patterns of behavior often emerge: players either converge rapidly to one of the stage game Nash equilibria and stay there or learn to coordinate their actions and alternate between the two Nash equilibria every other round. We show that IEL explains this behavior if the human subjects are truly in the dark and do not know or believe they know their opponent’s payoffs. To explain the behavior when agents are not in the dark, we need to modify the basic IEL model and allow some agents to begin with a good idea about how to play. We show that if the proportion of inspired agents with good ideas is chosen judiciously, the behavior of IEL agents looks remarkably similar to that of human subjects in laboratory experiments.     

Stakeholders’ relationships and product market competition

In this article, we study the relationships between main stakeholders (shareholders, consumers and employees) when firms are consumer oriented (CO) in the sense of caring about consumers’ interests in the objective function. We let these firms first bargain with labour union over their employees’ wages and then compete either in the quantity space (Cournot competition) or in the price space (Bertrand competition). Our model shows that taking care of the consumers’ interests when determining product market strategies may reverse the traditional ranking between Cournot and Bertrand equilibria. This implies that if shareholders in a CO firm can choose either a quantity or a price strategy, they will surprisingly choose the latter. Moreover, we show that the conflicting interests between main stakeholders are attenuated under Bertrand competition compared to Cournot competition.     

Delays and equilibria with large and small information in social learning

The general model of social learning with irreversible investment and endogenous timing is analyzed for any distribution of private informations. Strategic complementarities and multiple equilibria appear which are generated solely by information externalities. Different equilibria generate strikingly different amounts of information. The impacts of various assumptions (bounded beliefs, large number of agents, discrete time and short periods) are examined carefully. The properties are robust to the introduction of observation noise with a continuum of agents.     

Income distribution and equilibrium multiplicity in a stigma-based model of tax evasion

This paper incorporates continuous income distribution into the stigma-based model of tax compliance. The paper investigates the effect of income distribution on the existence of multiple equilibria, and characterizes the conditions under which multiple equilibria emerge. Precisely, multiple equilibria exist if taxpayer incomes are sufficiently homogeneous, because the ‘social coordination effect’ dominates the ‘individual characteristics effect’. Numerical simulations show that the main proposition is robust to allowing two-step audit policies on the part of the tax agency, under the presumption that the best (or good) equilibrium is selected whenever there are multiple equilibria. As a byproduct, the effect of various forms of tax reforms on the optimal two-step audit policy, the equilibrium compliance, and fiscal revenue is analyzed.     

A contraction principle for finite global games

I provide a new proof of uniqueness of equilibrium in a wide class of global games. I show that the joint best-response in these games is a contraction. The uniqueness result then follows as a corollary of the contraction principle. Furthermore, the contraction-mapping approach provides an intuition for why uniqueness arises: complementarities in games generate multiplicity of equilibria, but the global-games structure dampens complementarities so that only one equilibrium exists.     

Property rights and investments: An evolutionary approach

When contracts are not enforceable, or property rights are not clearly defined, individuals may lack an incentive to carry out costly investments even when they are socially efficient. Some recent contributions such as Ellingsen and Robles (2002) prove that this problem may be less dramatic than standard economic models would suggest. They propose evolutionary models in which only efficient equilibria can be (stochastically) stable. In this paper we show that these results are not robust with respect to the introduction of individual heterogeneity. When individuals have different cost functions, stochastically stable states may be inefficient, even when they induce a positive (suboptimal) level of investment.     

General equilibrium without utility functions: how far to go?

How far can we go in weakening the assumptions of the general equilibrium model? Existence of equilibrium, structural stability and finiteness of equilibria of regular economies, genericity of regular economies and an index formula for the equilibria of regular economies have been known not to require transitivity and completeness of consumers’ preferences. We show in this paper that if consumers’ non-ordered preferences satisfy a mild version of convexity already considered in the literature, then the following properties are also satisfied: (1) the smooth manifold structure and the diffeomorphism of the equilibrium manifold with a Euclidean space; (2) the diffeomorphism of the set of no-trade equilibria with a Euclidean space; (3) the openness and genericity of the set of regular equilibria as a subset of the equilibrium manifold; (4) for small trade vectors, the uniqueness, regularity and stability of equilibrium for two version of tatonnement; (5) the pathconnectedness of the sets of stable equilibria.     

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.     

Finding all equilibria in games of strategic complements

I present a simple and fast algorithm that finds all the pure-strategy Nash equilibria in games with strategic complementarities. This is the first non-trivial algorithm for finding all pure-strategy Nash equilibria.     

Mixed equilibria are unstable in games of strategic complements

In games with strict strategic complementarities, properly mixed Nash equilibria—equilibria that are not in pure strategies—are unstable for a broad class of learning dynamics.