Joel Sobel

Can We Trust Social Capital

This essay looks at the literature on social capital from the perspective of game theory. It reviews Bowling Alone by Robert Putnam and Social Capital: A Multifaceted Approach edited by Partha Dasgupta and Ismail Serageldin.

Equilibrium Selection in Signaling Games

The authors introduce a new solution concept, divine equilibrium, which refines the set of sequential equilibria in signaling games by requiring that off-the-equilibrium-path beliefs satisfy an additional restriction. This restriction rules out implausible sequential equilibria in examples. Divine equilibria exist because a sequential equilibrium that fails to be divine cannot be in a stable component. The authors demonstrate through examples that the stable component of signaling games is typically smaller than the set of divine equilibria and present a characterization of the set of stable outcomes in generic signaling games. Copyright 1987 by The Econometric Society.

Interdependent preferences and reciprocity

Experiments, ethnography, and introspection provide evidence economic agents do not act to maximize their narrowly defined self interest. Expanding the domain of preferences to include the utility of others provides a coherent way to extend rational choice theory.There are two approaches for including extended or social preferences in strategic models. One posits that agents have extended preferences, but maintains the conventional assumption that these preferences are stable. Prominent examples of this approach permit agents to exhibit concern for status, inequality, and social welfare. The other approach permits the strategic context to determine the nature of individual preferences. Context-dependent preferences can capture the possibility that agents are motivated in part by reciprocity. They may sacrifice personal consumption in order to lower the utility of unkind agents or to raise the utility of kind agents.This paper surveys the evidence in favor of social preferences and describes the implications of the leading theoretical models of extended preferences. It presents behavioral assumptions that characterize different types of social preferences. It investigates the extent to which social preferences may arise as the limit of evolutionary processes. It discusses the relationship between norms of reciprocity and social preferences in repeated interactions.

A Theory of Credibility

This paper presents models in which one agent must decide whether to trust another, whose motives are uncertain. Reliability can only be communicated through actions. In this context, it pays for people to build a reputation based on reliable behaviour; someone becomes credible by consistently providing accurate and valuable information or by performing useful services. The theory provides a justification for long-term arrangements without binding contracts. It also describes those situations where it pays an agent to cash in on his reputation.

Samurai Accountant: A Theory of Auditing and Plunder

A risk neutral principal wishes to exact a payment from a risk neutral agent whose wealth he does not know, but may verify through a costly auditing procedure. We characterize efficient schemes for the principal when he is allowed to choose schedules for preaudit and postaudit payments and audit probabilities, subject to the constraint that only monetary incentives can be used and that the principal may never make a net payment to the agent. The main results are that efficient schemes involve preaudit payments which are increasing in the agents wealth, audit probabilities are decreasing in the agents wealth and also satisfy certain constraints as equalities. In general, such schemes involve stochastic auditing and rebates after an audit.

Cyclic Pricing by a Durable Goods Monopolist

In the model of this paper a monopoly seller of a durable good holds periodic sales as a means of price discrimination. A new cohort of consumers enters the market in each period, interested in purchasing the good either immediately or after a delay. Within each cohort, consumers vary in their tastes for the good. Under broad conditions, the seller will vary the price over time. In most periods, he will charge a price just low enough to sell immediately to consumers with a high willingness to pay. Periodically, however, he will drop the price far enough to sell to an accumulated group of consumers with a low willingness to pay.

Strategic stability and uniqueness in signaling games

Abstract A class of signaling games is studied in which a unique Universally Divine equilibrium outcome exists. We identify a monotonicity property under which a variation of Universal Divinity is generically equivalent to strategic stability. Further assumptions guarantee the existence of a unique Universally Divine outcome.

The Timing of Sales

This paper presents a model of intertemporal price discrimination. A fixed number of sellers produce a homogeneous good. Consumers with different preferences enter the market in each period and leave when they make a purchase. The sellers typically vary their prices over time, charging a high price in most periods, but occasionally cutting the price to sell to a large group of customers with a low reservation price. In some equilibria, all stores lower their price at the same time and to the same level.

A Multistage Model of Bargaining

This paper presents a simple, multistage model of bargaining wherein a seller makes an offer that can be either accepted or refused. If rejected, the process continues. How the sellers ability to make commitments affects bargaining outcomes is analysed by comparing the commitment equilibria to those arising when commitment is impossible. The effects of increasing uncertainty about preferences and varying the length of the bargaining horizon are analysed. The ways in which the bargaining environment can be changed to improve outcomes are discussed.

Hierarchical design and enforcement of income tax policies

Abstract A hierarchical model of tax compliance is studied in which the government selects a tax policy and then delegates the responsibility to collect taxes to the IRS. There is a fixed distribution of income in the economy. Individuals differ by their income, which is known niether to the government nor to the IRS. We completely characterize the solution to the IRSs revenue-maximizing problem. When taxpayers are risk neutral, the optimal auditing policy divides the reported incomes into at most three groups. We show that the government provides a smaller budget to the IRS than the IRS would wish.