Jakub Steiner

Dynamic coordination with individual learning

We study coordination in dynamic global games with private learning. Players choose whether and when to invest irreversibly in a project whose success depends on its quality and the timing of investment. Players gradually learn about project quality. We identify conditions on temporal incentives under which, in sufficiently long games, players coordinate on investing whenever doing so is not dominated. Roughly speaking, this outcome occurs whenever playersʼ payoffs are sufficiently tolerant of non-simultaneous coordination. We also identify conditions under which players coordinate on the risk-dominant action. We provide foundations for these results in terms of higher order beliefs.

Reversibility in dynamic coordination problems

Agents at the beginning of a dynamic coordination process (1) are uncertain about actions of their fellow players and (2) anticipate receiving strategically relevant information later on in the process. In such environments, the (ir)reversibility of early actions plays an important role in the choice among them. We characterize the strategic eects of the reversibility option on the coordination outcome. Such an option can either enhance or hamper ecient coordination, and we determine the direction of the eect based only on simple features of the coordination problem. The analysis is based on a generalization of the Laplacian property known from static global games: players at the beginning of a dynamic game act as if they were entirely uninformed about aggregate play of fellow players in each stage of the coordination process.

Tractable dynamic global games and applications

We present a family of tractable dynamic global games and its applications. Agents privately learn about a fixed fundamental, and repeatedly adjust their investments while facing frictions. The game exhibits many externalities: payoffs may depend on the volume of investment, on its volatility, and on its concentration. The solution is driven by an invariance result: aggregate investment is (in a pivotal contingency) invariant to a large family of frictions. We use the invariance result to examine how frictions, including those similar to the Tobin tax, affect equilibrium. We identify conditions under which frictions discourage harmful behavior without compromising investment volume.

Coordination in a Mobile World

We study coordination failures in many simultaneously occurring coordination problems called projects. Players encounter one of these projects, but have an outside option to search for another of the projects. Drawing on the global games approach, we show that such a mobile game has a unique equilibrium which allows us to examine comparative statics. The endogeneity of the outside option value and of the search activity leads to non-monotonicity of welfare with respect to search costs; high mobility may hurt players. Moreover, outcomes of the mobile game are remarkably robust to changes in the exogenous parameters. In contrast to the “static” benchmark global game without a search option, successful coordination is frequent in the mobile game even for extremely poor distributions of economic fundamentals, and coordination failures are common even for extremely good distributions. The strategic consequences of the search option are robust to various modifications of the model.

Rational inattention dynamics: Inertia and delay in decision-making

We solve a general class of dynamic rational-inattention problems in which an agent repeatedly acquires costly information about an evolving state and selects actions. The solution resembles the choice rule in a dynamic logit model, but it is biased towards an optimal default rule that does not depend on the realized state. We apply the general solution to the study of (i) the sunk-cost fallacy; (ii) inertia in actions leading to lagged adjustments to shocks; and (iii) the tradeoff between accuracy and delay in decision-making.

The effects of risk preferences in mixed-strategy equilibria of 2×2 games

Abstract We consider the effects of risk preferences in mixed-strategy equilibria of 2 × 2 games, provided such equilibria exist. We identify sufficient conditions under which the expected payoff in the mixed equilibrium increases or decreases with the degree of risk aversion. We find that (at least moderate degrees of) risk aversion will frequently be beneficial in mixed equilibria.

Influential Opinion Leaders

We present a two-stage coordination game in which early choices of experts with special interests are observed by followers who move in the second stage. We show that the equilibrium outcome is biased toward the experts’ interests even though followers know the distribution of expert interests and can account for it when evaluating observed experts’ actions. Expert influence is fully decentralized in the sense that each individual expert has a negligible impact. The bias in favor of experts results from a social learning effect that is multiplied through a coordination motive. The total effect can be large even if the direct social learning effect is small. We apply our results to the onset of social movements and to the diffusion of products with network externalities.

Communication, Timing, and Common Learning

We study the effect of stochastically delayed communication on common knowledge acquisition (common learning). If messages do not report dispatch times, communication prevents common learning under general conditions even if common knowledge is acquired without communication. If messages report dispatch times, communication can destroy common learning under more restrictive conditions. The failure of common learning in the two cases is based on different infection arguments. Communication can destroy common learning even if it ends in finite time, or if agents communicate all of their information. We also identify conditions under which common learning is preserved in the presence of communication.

Sand in the Wheels: A Dynamic Global-Game Approach

We study the impact of frictions on the prevalence of systemic crises. Agents privately learn about a fixed payoff parameter, and repeatedly adjust their investments while facing transaction costs in a dynamic global game. The model has a rich structure of externalities: payoffs may depend on the volume of aggregate investment, on the concentration of investment, or on its volatility. We examine how small frictions, including those similar to the Tobin tax, affect the equilibrium. We identify conditions under which frictions discourage harmful behavior without compromising investment volume. The analysis is driven by a robust invariance result: the volume of aggregate investment (measured in a pivotal contingency) is invariant to a large family of frictions.

Learning by Similarity in Coordination Problems

We study a learning process in which subjects extrapolate from their experience of similar past strategic situations to the current decision problem. When applied to coordination games, this learning process leads to contagion of behavior from problems with extreme payoffs and unique equilibria to very dissimilar problems. In the long-run, contagion results in unique behavior even though there are multiple equilibria when the games are analyzed in isolation. Characterization of the long-run state is based on a formal parallel to rational equilibria of games with subjective priors. The results of contagion due to learning share the qualitative features of those from contagion due to incomplete information, but quantitatively they differ.