Abstract

We study how the random assignment of new students to introductory-week groups shapes subsequent friendship networks. Both women and men report being much more likely to be friends with same-gender students with whom they were (randomly) assigned in a group during their first week on campus, and the effect is much stronger for women. When students from the same cohort play a repeated trust game in the experimental laboratory, their behavior helps explain what we observed in the field. Women display more stability and less flexibility than men in their interactions with individuals with whom they had previously played. This difference is enough to generate homophily in the observational data even though subjects show no intrinsic preference for same-gender interaction.

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