Braz Camargo

Trading Dynamics in Decentralized Markets with Adverse Selection

The authors study a dynamic, decentralized lemons market with one-time entry and characterize its set of non-stationary equilibrium. This framework offers a theory of how a market suffering from adverse selection recovers over time endogenously; given an initial fraction of lemons, the model provides sharp predictions about how prices and the composition of assets evolve over time. Comparing economies in which the initial fraction of lemons varies, the authors study the relationship between the severity of the lemons problem and market liquidity. They use this framework to understand how asymmetric information contributed to the breakdown in trade of asset{backed securities during the recent financial crisis, and to evaluate the efficacy of one policy that was implemented in attempt to restore liquidity.

Interracial Friendships in College

We use unique longitudinal data to provide direct evidence about interracial friendships at different stages of college and to provide new evidence about some of the reasons for the observed patterns of interaction. We find that, while much sorting exists at all stages of college, black and white students are, in reality, very compatible as friends; randomly assigned roommates of different races are as likely to become friends as randomly assigned roommates of the same race. Further, we find that, in the long run, being (randomly) assigned a black roommate significantly increases the number of other black friends a white student has.

Good news and bad news in two-armed bandits

Abstract This note provides a characterization of optimal policies in a class of two-armed bandits that allows for correlated arms. This characterization extends previously known results in the literature. In particular, it implies, under a mild continuity assumption, the optimality of cutoff belief strategies for this class of bandits. Cutoff beliefs are not unique, though.

Subsidizing Price Discovery

When markets freeze, not only are gains from trade left unrealized, but the process of information production through prices, or price discovery, is disrupted as well. Though this latter effect has received much less attention than the former, it constitutes an important source of inefficiency during times of crisis. We provide a formal model of price discovery and use it to study a government program designed explicitly to restore the process of information production in frozen markets. This program, which provided buyers with partial insurance against acquiring low-quality assets, reveals a fundamental trade-off for policymakers: while some insurance encourages buyers to bid for assets when they otherwise would not, thus promoting price discovery, too much insurance erodes the informational content of these bids, which hurts price discovery.

Learning in society

In the canonical learning model, the multi-armed bandit with independent arms, a decision maker learns about the different alternatives only through his private experience. It is well known that any optimal experimentation strategy for this problem is ex-post inefficient: it sometimes leads the superior alternative to be dropped altogether. Many situations of interest, however, involve learning from individual experience and the experience of others. This paper shows how learning in society can overcome this inefficiency. We consider an economy populated with a continuum of infinitely lived agents where each one of them faces a multi-armed bandit. The unknown stochastic payoffs of each arm are the same for all agents. In each period, they are randomly and anonymously matched in pairs, and in any such match they observe their partners current action choice and its outcome. We establish that if initial beliefs are sufficiently heterogeneous, then the fraction of the population choosing the superior arm converges to one in any perfect bayesian equilibrium of this game. We also show that the same conclusion holds when only action choices are observable within a match and the number of arms is two

Endogenous supply of fiat money

We consider whether reputation concerns can discipline the behavior of a long-lived self-interested agent who has a monopoly over the provision of fiat money. We obtain that when this agent can commit to a choice of money supply, there is a monetary equilibrium where it never overissues. We show, however, that monetary equilibria with no overissue do not exist when there is no commitment. This happens because the incentives this agent has to maintain a reputation for providing valuable currency disappear once its reputation is high enough. More generally, we prove that in the absence of commitment overissue happens infinitely often in any monetary equilibrium. We conclude by showing that imperfect memory can restore the positive result obtained with commitment.

Learning-by-Employing: The Value of Commitment under Uncertainty

We analyze commitment to employment in an environment in which an infinitely lived firm faces a sequence of finitely lived workers who differ in their ability. A worker’s ability is initially unknown, and a worker’s effort affects how informative about ability the worker’s performance is. We show that equilibria display commitment to employment only when effort has a delayed impact on output. In this case, insurance against early termination encourages workers to exert effort, thus allowing the firm to better identify workers’ ability. Our results help explain the use of probationary appointments in environments in which workers’ ability is uncertain.