Learning to play Bayesian games

This paper discusses the implications of learning theory for the analysis of games with a move by Nature. One goal is to illuminate the issues that arise when modeling situations where players are learning about the distribution of Nature's move as well as learning about the opponents' strategies. A second goal is to argue that quite restrictive assumptions are necessary to justify the concept of Nash equilibrium without a common prior as a steady state of a learning process.     

Probabilistic sophistication and variational preferences

This paper shows that in the class of variational preferences the notion of probabilistic sophistication is equivalent to expected utility as long as there exists at least one event such that the independence axiom holds for bets on that event. This extends the result of Marinacci (2002) [13] and provides a novel interpretation of his result.     

Sex and environmental policy in the U.S. House of Representatives

Using LCV score data, we find that female legislators favor stricter environmental policies than do their male counterparts. Moreover, gender-corrected estimates suggest that voters do not push environmental policy towards the middle, but rather select the ideologically closest candidate.     

Error cascades in observational learning: An experiment on the Chinos game

The paper reports an experimental study based on a variant of the popular Chinos game, which is used as a simple but paradigmatic instance of observational learning. There are three players, arranged in sequence,each of which wins a fixed price if she manages to guess the total number of coins lying in everybody?s hands. Our evidence shows that, despite the remarkable frequency of equilibrium outcomes, deviations from optimal play are also significant. And when such deviations occur, we find that, for any given player position, the probability of a mistake is increasing in the probability of a mistake of her predecessors. This is what we call an error cascade, which we measure by evaluating the (heterogeneous) Quantal Response Equilibrium which better suits our data. We also check the robustness of our findings when we allow for belief heterogeneity by applying Kübler and Weizsäcker?s (2004) cognitive frame of limited depth of reasoning.     

The robustness of robust implementation

We show that a mechanism that robustly implements optimal outcomes in a one-dimensional supermodular environment continues to robustly implement ε-optimal outcomes in all close-by environments. Robust implementation of ε-optimal outcomes is thus robust to small perturbations of the environment. This is in contrast to ex-post implementation which is not robust in this sense as only trivial social choice functions are ex-post implementable in generic environments.     

Regret-based continuous-time dynamics

Regret-based dynamics have been introduced and studied in the context of discrete-time repeated play. Here we carry out the corresponding analysis in continuous time. We observe that, in contrast to (smooth) fictitious play or to evolutionary models, the appropriate state space for this analysis is the space of distributions on the product of the players' pure action spaces (rather than the product of their mixed action spaces). We obtain relatively simple proofs for some results known in the discrete case (related to ‘no-regret’ and correlated equilibria), and also a new result on two-person potential games (for this result we also provide a discrete-time proof).     

Optimal advertising of auctions

We study a symmetric independent private values auction model where the revenue-maximizing seller faces a cost cn of attracting n bidders to the auction. If the distribution of valuations possesses an increasing failure rate (IFR), the seller overinvests in attracting bidders compared to the social optimum. Conversely, if the distribution is DFR, the seller underinvests compared to the social optimum. If the distribution of valuations becomes more dispersed, both, a revenue- and a welfare-maximizing seller, attract more bidders.     

Premium auctions and risk preferences

In a premium auction, the seller offers some “payback”, called premium, to a set of high bidders at the end of the auction. This paper investigates how the performance of such premium tactics is related to the bidders? risk preferences. We analyze a two-stage English premium auction model with symmetric interdependent values, in which the bidders may be risk averse or risk preferring. Upon establishing the existence and uniqueness of a symmetric equilibrium, we show that the premium causes the expected revenue to increase in the bidders? risk tolerance. A “net-premium effect” is key to this result.     

Rents, military elites, and political democracy

In autocratic regimes the military elite is in a position to extract rents, because without the support of the military the government is in general not able to sustain itself. In this paper, we empirically confirm the negative relation between transfers to the military and the degree of democracy for developing countries. We use an instrumental variable approach to account for the simultaneity that arises since the degree of democracy is itself a function of transfers to the military.     

A dynamic model of unsecured credit

We study the terms of credit in a competitive market in which sellers (lenders) are willing to repeatedly finance the purchases of buyers (borrowers) by engaging in a credit relationship. The key frictions are: (i) the lender cannot observe the borrower?s ability to repay a loan; (ii) the borrower cannot commit to any long-term contract; (iii) it is costly for the lender to contact a borrower and to walk away from a contract; and (iv) transactions within each credit relationship are not publicly observable. The lender?s optimal contract has two key properties: delayed settlement and debt forgiveness. Finally, we study the impact of changes in the initial cost of lending on the contract terms.     

Informational size and incentive compatibility with aggregate uncertainty

In McLean and Postlewaite (Econometrica 56, 1992, p. 2421), we analyzed pure exchange economies with asymmetrically informed agents. We defined a notion of informational size and showed that, when the aggregate information of all agents resolves nearly all the uncertainty regarding the state of nature, the conflict between incentive compatibility and (ex post) efficiency can be made small if agents have sufficiently small informational size. This paper investigates the relationship between informational size and efficiency for the case in which nontrivial aggregate uncertainty is present, i.e., when significant uncertainty about the world persists even when the information of all agents is known.     

Choosing and sharing

Implementing a project, like a nationwide nuclear waste disposal, which benefits all involved agents but brings major costs only to the host is often problematic. In practice, revelation issues and redistributional concerns are significant obstacles to achieving stable agreements. We address these issues by proposing the first mechanism to select the efficient site (the host with the lowest cost) while simultaneously allowing for the implementation of any individually rational division of the whole hosting cost. The subgame perfect Nash equilibria of our simple mechanism are efficient, budget-balanced and individually rational. Moreover, the truthful equilibrium is immune to coalitional deviations.     

Income distributions and decomposable divergence measures

Inequality indices evaluate the divergence between the income distribution and the hypothetical situation where all individuals receive the mean income, and are unambiguously reduced by a Pigou–Dalton progressive transfer. This paper proposes a new approach to evaluate the divergence between any two income distributions, where the latter can be a reference distribution for the former. In the case where the reference distribution is perfectly egalitarian – and uniquely in this case – we assume that any progressive transfer reduces the divergence, and that the divergence can be additively separated into inequality and efficiency loss. We characterize the unique class of decomposable divergence measures consistent with these views. We derive the associated relative and absolute subclasses, and we illustrate the applicability of our results. This approach extends the generalized entropy studied in inequality measurement.     

Voting blocs, party discipline and party formation

I study the strategic incentives to coordinate votes in an assembly. Coalitions form voting blocs, acting as single players and affecting the policy outcome. In an assembly with two exogenous parties I show how the incentives to accept party discipline depend on the types of the agents, the sizes of the parties, and the rules the blocs use to aggregate preferences. In a game of fully endogenous party formation, I find sufficient conditions for the existence of equilibria with one bloc, two blocs, and multiple blocs.     

Pre-sale information

In markets as diverse as that for specialized industrial equipment or that for retail financial services, sellers or intermediaries may earn profits both from the sale of products and from the provision of pre-sale consultation services. We study how a seller optimally chooses the costly quality of pre-sale information, next to the price of information and the product price, and obtain clear-cut predictions on when information is over- and when it is underprovided, even though we find that information quality does not satisfy a standard single-crossing property. Buyers who are a priori more optimistic about their valuation end up paying a higher margin for information but a lower margin for the product when they subsequently exercise their option to purchase at a pre-specified price.     

Misery loves company: Social regret and social interaction effects in choices under risk and uncertainty

Extensive field evidence shows individuals? decisions in settings involving uncertainty depend on their peers? decisions. One hypothesized cause of peer group effects is social interaction effects: an individual?s utility from an action is enhanced by others taking the same action. We employ a series of controlled laboratory experiments to study the causes of peer effects in choice under uncertainty. We find strong peer group effects in the laboratory. Our design allows us to rule out social learning, social norms, group affiliation, and complementarities as possible causes for the observed peer group effects, leaving social interaction effects as the likely cause. We use a combination of theory and empirical analysis to show that preferences including “social regret” are more consistent with the data than preferences including a taste for conformity. We observe spillover effects, as observing another?s choice of one risky gamble makes all risky gambles more likely to be chosen.     

The econometric critique of computable general equilibrium modeling: the role of functional forms

Computable general equilibrium (CGE) models are among the most influential tools in applied economics. However, some serious questions have been raised about the empirical validity of these models. The core of the critique is that the parameter selection criteria are unsound and the use of first-order (CES class) functional forms imposes influential restrictions on the model's structure. A formal summary of the case against standard CGE modeling is presented, as is an alternative econometric-based modeling strategy which answers the critique. We then present a comparative CGE modeling experiment designed to assess the role of function forms. It is found that choice of functional forms affects not only industry-specific results, but aggregate results as well, even for small policy shocks.     

A model of fashions and status

This paper presents a model of fashion cycles based on the idea that individuals purchase fashion goods because their displayed status increases with the personal status of other consumers who buy the same good. Fashion cycles occur in the model because demand now is a rising function of future prices: if future prices are high, only rich consumers will buy it in the future and the good will have a higher status value in the future and will be more desirable now, even though demand now is a decreasing function of current price. The time inconsistency problem is solved by repeated cycles which allows for reputation building. The crucial assumption made is that there is perfect information about the price path of all firms and the average status of the purchasers of each product. This limits possible profits in fashion markets in competition as imitation of price paths is then possible.     

The real puzzle of blackmail: An informational approach

The “puzzle” of blackmail is that threats to reveal private information that would be harmful to someone in exchange for money are illegal, but revelation is not. The resolution is that concealment of information about product quality impedes the efficient operation of markets, whereas revelation promotes it. The real puzzle is why possessors are not naturally inclined to sell to uninformed parties, who value the information more than would-be blackmail victims. The answer has to do with the public good qualities of information, which create an appropriability problem in transactions with uninformed parties. The paper also discusses incentives to acquire compromising information.