Researchers using directed network data to estimate peer effects must somehow handle unreciprocated nominations. To better understand how peer effects operate and how best to estimate their effects, this paper investigates how the reciprocation of friendship mediates peer effects. We begin by...

The belief that people are affected by the groups in which they are active has long led policy makers to manipulate the groups to which people are exposed. This paper studies the optimal design of groups to maximize racial and ethnic integration. We show that the group composition that maximizes...