I develop a model of (individually rational) collective reality denial in groups, organizations and markets. Whether participants' tendencies toward wishful thinking reinforce or dampen each other is shown to hinge on a simple and novel mechanism. When an agent can expect to benefit from other's...

A brief discussion of recent methods using the Hat Matrix for identifying leverage points, and clustering techniques for finding groups of data points is presented. The problem of identifying leverage groups is addressed, and a heuristic algorithm for identifying both leverage points and...

Committees improve decisions by pooling independent information of members, but promote manipulation, obfuscation, and exaggeration of private evidence when members have conflicting preferences. We study how self-interest mediates these conflicting forces. When members' preferences differ, no...

This paper studies both theoretically and empirically the determinants of group formation and of the degree of participation when the population is heterogeneous, both in terms of income and race or ethnicity. We are especially interested in whether and how much the degree of heterogeneity in...

Scholars have pointed to ethnic and other social divisions as a leading cause of economic underdevelopment, due in part to their adverse effects on public good provision and collective action. We investigate this issue in post-war Sierra Leone, one of the world's poorest countries. To address...

We develop a Roy model of social interactions in which individuals sort into peer groups based on comparative advantage. Two key results emerge: First, when comparative advantage is the guiding principle of peer group organization, the effect of moving a student into an environment with...

This paper develops a model of social interactions and endogenous poverty traps. The key idea is captured in a framework in which the likelihood of future social interactions with members of one%u2019s group is partly determined by group-specific investments made by individuals. I prove three...

We study a dynamic model of environmental protection in which the level of pollution is a state variable that strategically links policy making periods. Policymakers are forward looking but politically motivated: they have heterogeneous preferences and do not fully internalize the cost of...