How Do Friendships Form?

We examine how people form social networks among their peers. We do this by using a unique dataset that tells us the volume of email between any two people in the sample. The data are from students and recent graduates of Dartmouth College. The data are consistent with a model in which the expected value of a social interaction with an unknown person is low relative to travel costs and the benefits from interacting with the same person repeatedly are high. First year students interact with whomever is in their immediate proximity and form long term friendships with a subset of those people. Geographic proximity and race are even greater determinants of social interaction than are common interests, majors, or family background. Two randomly chosen white students interact three times more often than do a black student and a white student. However, placing the black and white student in the same freshman dorm increases their frequency of interaction by a factor of three. We show that a traditional linear in means model of social interaction can be a good approximation to the actual set of social interactions if researchers condition on key factors like distance, race and age.