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Social Interactions and Endogenous Association March 2005 PRELIMINARY

This paper develops a model of social interactions with endogenous associations. People are assumed to invest time to develop the relationships that maximize their utility. When associations are endogenous, the effects of groups on individual behavior will be nonlinear even when the underlying behavioral model is linear; improving the performance of some members of the group may hurt others; and peer pressure emerges with people taking actions to make others want to interact with them. Using data on associations among high school students, we provide a range of evidence consistent with our model. Individuals associate with people whose behaviors and characteristics are similar to their own. This tendency is particularly strong when the pool of similar potential associates is larger and when the size of the group is larger. I appreciate helpful comments from Larry Blume, Ed Glaeser, Kevin Lang, and Qingyan Shang and from participants at the 2005 AEA Meetings and the University of Alabama. Qingyan Shang provided excellent research assistance. I am also grateful for support from the Mershon Center at Ohio State University and the NBER, where much of the work on this paper was done. I am, of course, solely responsible for all errors.