This paper provides an analysis of aggregate behavioral outcomes when individual utility exhibits social interaction effects. We study generalized logistic models of individual choice which incorporate terms reflecting the desire of individuals to conform to the behavior of others in an environment of noncooperative decisionmaking. Laws of large numbers are generated in such environments. Multiplicity of

Economists have long been ambivalent about whether the discipline should focus on the analysis of markets or should be concerned with social interactions more generally. Recently the discipline has sought to broaden its scope while maintaining the rigor of modern economic analysis. Major theoretical developments in game theory, the economics of the family, and endogenous growth theory have taken place. Economists have also performed new empirical research on social interactions, but the empirical literature does not show progress comparable to that achieved in economic theory. This paper examines why and discusses how economists might make sustained contributions to the empirical analysis of social interactions.

This paper presents on overview of the economics that lies behind social interaction models and briefly discusses the empirical approaches to social interactions. We present a simple model with local interactions, similar to Glaeser, Sacerdote and Scheinkman (1996) but using a continuous action space and starting with optimizing behavior. We then extend the model to include both global and local interactions. We suggest and use a methodology for using variation of intra-city aggregates to identify the relative sizes of local and global interactions. We also present a model with endogenous location choice and use the predictions of that model to identify the sources of cross-city variance that are due to sorting and interaction. Finally, we present a brief discussion of using time-series to estimate the social interactions in broad aggregates.

Most contracts, whether between voters and politicians or between house owners and contractors, are incomplete. “More law,” it typically is assumed, increases the likelihood of contract performance by increasing the probability of enforcement and/or the cost of breach. This paper studies a contractual relationship where the first mover has to decide whether she wants to enter a contract without knowing whether the second mover will perform. We analyze how contract enforceability affects individual performance for exogenous preferences. Then we apply a dynamic model of preference adaptation and find that economic incentives have a non–monotonic impact on behavior. Individuals perform a contract when enforcement is strong or weak but not with medium enforcement probabilities: Trustworthiness is “crowded in” with weak and “crowded out” with medium enforcement. In a laboratory experiment we test our model’s implications and find support for the crowding prediction. Our finding is in line with the recent work on the role of contract enforcement and trust in formerly Communist countries.

A central idea in marketing and diffusion research is that influentials—a minority of individuals who influence an exceptional number of their peers—are important to the formation of public opinion. Here we examine this idea, which we call the “influentials hypothesis,” using a series of computer simulations of interpersonal influence processes. Under most conditions that we consider, we find that large cascades of influence are driven not by influentials, but by a critical mass of easily influenced individuals. Although our results do not exclude the possibility that influentials can be important, they suggest that the influentials hypothesis requires more careful specification and testing than it has received.

During the last two decades economists have made much progress in understanding incentives, contracts and organizations. Yet, they constrained their attention to a very narrow and empirically questionable view of human motivation. The purpose of this paper is to show that this narrow view of human motivation may severely limit understanding the determinants and effects of incentives. Economists may fail to understand the levels and the changes in behaviour if they neglect motives like the desire to reciprocate or the desire to avoid social disapproval. We show that monetary incentives may backfire and reduce the performance of agents or their compliance with rules. In addition, these motives may generate very powerful incentives themselves.

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We conducted a natural field experiment to explore the effect of price changes on charitable contributions. To operationalize our tests, we examine whether an offer to match contributions to a non-profit organization changes the likelihood and amount that an individual donates. Direct mail solicitations were sent to over 50,000 prior donors. We find that the match offer increases both the revenue per solicitation and the probability that an individual donates. While comparisons of the match treatments and the control group consistently reveal this pattern, larger match ratios (i.e., $3:$1 and $2:$1) relative to smaller match ratios ($1:$1) had no additional impact. The results have clear implications for practitioners in the design of fundraising campaigns and provide avenues for future empirical and theoretical work on charitable giving. Further, the data provide an interesting test of important methods used in cost-benefit analysis.

We develop a theory of prosocial behavior that combines heterogeneity in individual altruism and greed with concerns for social reputation or self-respect. Rewards or punishments (whether material or imagerelated) create doubt about the true motive for which good deeds are performed and this “overjustification effect ” can induce a partial or even net crowding out of prosocial behavior by extrinsic incentives. We also identify the settings that are conducive to multiple social norms and more generally those that make individual actions complements or substitutes, which we show depends on whether stigma or honor is (endogenously) the dominant reputational concern. Finally, we analyze the socially optimal level of incentives and how monopolistic or competitive sponsors depart from it. Sponsor competition is shown to potentially reduce social welfare. Keywords:

We examine, experimentally and theoretically, how communication within a partnership may mitigate the problem (highlighted in contract theory) of hidden action. What is the form and content of the communication? Which model of decision-making can capture the impact of communication? We consider free-form communication, measure beliefs (about actions and beliefs), and examine which motivational forces influence subjects. We find they harbor belief-dependent preferences that can be captured using psychological game theory. In particular, agents are influenced by guilt aversion, which suggests a theory of why and how communication influences behavior in which statements of intent and resulting expectations play a special role. This has bearing on how to understand partnerships and contracts.