A Simple Exposition of Belief-Free Equilibria in Repeated Games

Recently, there has been made a substantial progress in the analysis of repeated games with private monitoring. This progress began with introducing a new class of sequential equilibrium strategies, called belief-free equilibria, that can be analyzed using recursive techniques. The purpose of this paper is to explain the general method of constructing belief-free equilibria, and the limit (or bound) on the set of payoff vectors that can be achieved in these strategies in a way that should be easily accessible, even for those who do not pretend to be experts in repeated games.

A nonmanipulable test

A test is said to control for type I error if it is unlikely to reject the data-generating process. However, if it is possible to produce stochastic processes at random such that, for all possible future realizations of the data, the selected process is unlikely to be rejected, then the test is said to be manipulable. So, a manipulable test has essentially no capacity to reject a strategic expert. Many tests proposed in the existing literature, including calibration tests, control for type I error but are manipulable. We construct a test that controls for type I error and is nonmanipulable.Comment: Published in at http://dx.doi.org/10.1214/08-AOS597 the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Strategic Manipulation of Empirical Tests

Theories can be produced by individuals seeking a good reputation of knowledge. Hence, a significant question is how to test theories anticipating that they might have been produced by (potentially uninformed) experts who prefer their theories not to be rejected. If a theory that predicts exactly like the data generating process is not rejected with high probability then the test is said to not reject the truth. On the other hand, if a false expert, with no knowledge over the data generating process, can strategically select theories that will not be rejected then the test can be ignorantly passed. These tests have limited use because they cannot feasibly dismiss completely uninformed experts. Many tests proposed in the literature (e.g., calibration tests) can be ignorantly passed. Dekel and Feinberg (2006) introduced a class of tests that seemingly have some power of dismissing uninformed experts. We show that some tests from their class can also be ignorantly passed. One of those tests, however, does not reject the truth and cannot be ignorantly passed. Thus, this empirical test can dismiss false experts.We also show that a false reputation of knowledge can be strategically sustained for an arbitrary, but given, number of periods, no matted which test is used (provided that it does not reject the truth). However, false experts can be discredited, even with bounded data sets, if the domain of permissible theories is mildly restricted.

Falsifiability

We examine the fundamental concept of Popper’s falsifiability within an economic model in which a tester hires a potential expert to produce a theory. Payments are made contingent on the performance of the theory vis-a-vis future realizations of the data. We show that if experts are strategic, then falsifiability has no power to distinguish legitimate scientific theories from worthless theories. We also show that even if experts are strategic there are alternative criteria that can distinguish legitimate from worthless theories.Testing Strategic Experts

Folk theorems with Bounded Recall under(Almost) Perfect Monitoring

A strategy profile in a repeated game has bounded recall L if play under the profile after two distinct histories that agree in the last L periods is equal. Mailath and Morris (2002, 2006) proved that any strict equilibrium in bounded-recall strategies of a game with full support public monitoring is robust to all perturbations of the monitoring structure towards private monitoring (the case of almost-public monitoring), while strict equilibria in unbounded-recall strategies are typically not robust. We prove that the perfect-monitoring folk theorem continues to hold when attention is restricted to strategies with bounded recall and the equilibrium is essentially required to be strict. The general result uses calendar time in an integral way in the construction of the strategy profile. If the players’ action spaces are sufficiently rich, then the strategy profile can be chosen to be independent of calendar time. Either result can then be used to prove a folk theorem for repeated games with almost-perfect almost-public monitoring.Repeated games, bounded recall strategies, folk theorem, imperfect monitoring