Making friends: A nonexperimental analysis of social pair formation
利用大学生从随机分配宿舍到自主选择室友的独特数据，分析友谊形成中的相似性偏好，发现能力、社会因素和运气共同影响交友选择。
Economists and psychologists often assume that people sort into groups based on similarities. In this article, the validity of this assumption is examined using pairwise data and a new application of a proven analytical technique. I use a unique administrative data set that follows undergraduate students as they move from quasi-randomly assigned housing into self-selected residence groups; social pair formation is measured using behavior, not survey responses. Sorting is observed from the baseline ‘clean slate’ of random groupings, creating a quasi-experimental environment and circumventing problems inherent in examining selection processes when starting groups are not randomly formed. A wide array of covariates, including original campus location, race, and academic ability is exploited to determine the most important factors driving students’ choices about with whom to live. Results support a role for ability in friendship formation, both conditionally and unconditionally, but also a significant and more potent influence of social factors and luck. The article demonstrates a novel approach to the analysis of normally unobserved human sorting processes in a real-world context.