We model a market populated by two groups of boundedly rational agents: “newswatchers” and “momentum traders.” Each newswatcher observes some private information, but fails to extract other newswatchers’ information from prices. If information diffuses gradually across the population, prices underreact in the short run. The underreaction means that the momentum traders can profit by trendchasing. However, if they can only implement simple (i.e., univariate) strategies, their attempts at arbitrage must inevitably lead to overreaction at long horizons. In addition to providing a unified account of under- and overreactions, the model generates several other distinctive implications.

Recent developments in computer networks have driven the cost of distributing information virtually to zero, creating extraordinary opportunities for sharing product evaluations. We present pricing and subsidy mechanisms that operate through a computerized market and induce the efficient provision of evaluations. The mechanisms overcome three major challenges: first, evaluations, which are public goods, are likely to be underprovided; second, an inefficient ordering of evaluators may arise; third, the optimal quantity of evaluations depends on what is learned from the initial evaluations. Keywords: evaluations, information sharing, product quality, computer network, market (JEL D70, D83, H41, L15) 2 Subjective evaluations by others are a valuable tool for consumers who are choosing which products to buy or how to spend their time. For example, we read magazines devoted to product evaluation before purchasing cars and appliances. We ask our friends and read reviews by professional cr...

This paper presents a dynamic, stochastic game-theoretic model of financial fragility. The model has two essential features. First, interrelated portfolios and payment commitments forge financial linkages among agents. Second, iid shocks to investment projects ’ operations at a single date cause some projects to fail. Investors who experience losses from project failures reallocate their portfolios, thereby breaking some linkages. In the Pareto-efficient symmetric equilibrium studied, two related types of financial crises can occur in response. One occurs gradually as defaults spread, causing even more links to break. An economy is more fragile ex post the more severe this financial crisis. The other type of crisis occurs instantaneously when forward-looking investors preemptively shift their wealth into a safe asset in anticipation of the contagion affecting them in the future. An economy is more fragile ex ante the earlier all of its linkages break from such a crisis. The paper also considers whether fragility is worse for larger economies.

There is growing evidence that consumers are influenced by Internet-based opinion forums before making a variety of purchase decisions. Firms whose products are being discussed in such forums are therefore tempted to manipulate consumer perceptions by posting costly anonymous messages that praise their products. This paper offers a theoretical analysis of the impact of such behavior on firm profits and consumer surplus. There are three main results. First, if every firm’s manipulation strategy is a monotonically increasing (decreasing) function of that firm’s true quality, strategic manipulation of online forums increases (decreases) the information value of a forum to consumers. This result implies the existence of settings where online forum manipulation benefits consumers. Second, equilibria where strategies are monotonically increasing (decreasing) functions of a firm’s true quality exist in settings where the firm’s net payoff function, inclusive of the cost of manipulation, is supermodular (submodular) in the firm’s quality and manipulation action. Third, in a broad class of settings, if the precision of honest consumer opinions that firms manipulate is sufficiently high, firms of all types, as well as society, would be strictly better off if manipulation of online forums was not possible. Nonetheless, firms are locked into a “rat race” and forced to spend resources on such profit-reducing activities; if they don’t, consumer perceptions will be biased against them. The social cost of online manipulation can be reduced by developing “filtering” technologies that make it costlier for firms to manipulate. Interestingly, as the amount of user-contributed online content increases, it is firms, and not consumers, that have most to gain from the development of such technologies.

Information regarding economic fundamentals is widely dispersed in society, is only imperfectly aggregated through prices or other indicators of aggregate activity, and can not be centralized by the government or any other institution. In this paper we seek to identify policies that can improve the decentralized use of such dispersed information without requiring the government to observe this information. We show that this can be achieved by appropriately designing the contingency of taxation on ex-post public information regarding the realized fundamentals and aggregate activity. When information is common (as in the Ramsey literature) or when agents have private information only about idiosyncratic shocks (as in the Mirrlees literature), the contingency on fundamentals alone suffices for efficiency. When instead agents have private information about aggregate shocks, the contingency on aggregate activity is crucial. An appropriate combination of the two contingencies permits the government to: (i) dampen the impact of noise and hence reduce non-fundamental volatility, without also dampening the impact of fundamentals; (ii) induce agents to internalize informational externalities, and hence improve the speed of social learning; (iii) restore a certain form of constrained efficiency in the

Multiplicity of solutions is typical to systems where the individual’s tendency to act in a certain way increases when more of the other individuals in the population act in this way. We provide a detailed analysis of a queueing model in which two priority levels can be purchased. In particular, we compute all of the Nash equilibrium strategies (pure and mixed) of the threshold type. OR/MS classification: Queues: Priority. Games/group decisions: Noncooperative. 1

The arrival of new, unfamiliar, investment opportunities is often associated with “exuberant” movements in asset prices and real economic activity. During these episodes of high uncertainty, financial markets look at the real sector for signals about the profitability of the new investment opportunities, and vice versa. In this paper, we study how such information spillovers impact the incentives that agents face when making their real economic decisions. On the positive front, we find that the sensitivity of equilibrium outcomes to noise and to higher-order uncertainty is amplified, exacerbating the disconnect from fundamentals. On the normative front, we find that these effects are symptoms of constrained ineffi ciency; we then identify policies that can improve welfare without requiring the government to have any informational advantage vis-a-vis the market. At the heart of these results is a distortion that induces a conventional neoclassical economy to behave as a Keynesian “beauty contest”and to exhibit fluctuations that may look like “irrational exuberance”to an outside observer.

This paper provides a norm-based explanation for two features of the fertility transition that have been observed in many different settings: the slow response to external interventions and the wide variation in the response to the same intervention. Most societies have traditionally put norms into place to regulate fertility. When the economic environment changes, individuals gradually learn through their social interactions about the new reproductive equilibrium that will emerge in their community. This characterization of the fertility transition as a process of changing social norms is applied to rural Bangladesh, where norms are organized at the level of the religious group and interactions rarely cross religious boundaries. Consistent with the view that changing social norms are driving changes in reproductive behavior in these communities, we find that the individual’s contraception decision responds strongly to changes in contraceptive prevalence in her own religious group within the village whereas cross-religion effects are entirely absent. Local changes in reproductive behavior occur independently across religious groups despite the fact that all individuals in the village have access to the same family planning inputs.

Efficiently handling reputation is important in dealing with free-riding, malicious attacks and random failures in selforganized communication systems. At the same time, work in this context is often found to be relevant in many other disciplines, in particular the social sciences. A number of distributed reputation systems have been proposed and analyzed, although research has not been very coherent. In this paper, for the first time, we provide an overview of the stateof-the-art in the various computer science communities as well as the social sciences. In particular, we present results obtained from our mathematical model devised to investigate the impact of liars on their peers ’ reputation about a subject. We find that liars have no impact unless their number exceeds a certain threshold (phase transition). We give precise formulae and quantify the impact, thereby providing insight into fundamental questions in social networks as well as facilitating performance evaluation and optimization of distributed reputation systems in communication networks. We conclude by suggesting fundamental directions for future research into reputation. Categories and Subject Descriptors C.2.1 [Computer-communication networks]: Network architecture and design—Distributed networks; D.2.4 [Computer-communication networks]: Distributed systems—

Promising emerging equity markets often witness investment herds and frenzies, accompanied by an abundance of media coverage. Complementarity in information acquisition can explain these anomalies. Because information has a high fixed cost of production, its equilibrium price is low when quantity is high. Investors all buy the most popular information because it has the lowest price. Given two identical asset markets, investors herd: asset demand is higher in the market with abundant information because information reduces risk. By lowering risk, information raises the asset’s price. Transitions between low-information/low-asset-price and high-information/high-asset-price equilibria raise price volatility and create price paths resembling periodic frenzies. Using equity data and a new panel data set of news counts for 23 emerging markets, the results show that when asset market volatility increases, news coverage intensifies, and that more news is correlated with higher asset prices.