Friendship Networks and Political Opinions

We examine how social interactions and friendships shape students' political opinions in a natural experiment at Sciences Po, a leading French university specializing in social and political sciences. The quasi-random assignment of students into short-term integration groups before their academic curriculum reduces political opinion gaps and fosters friendship formation. Using same-group membership as an instrumental variable for friendship, we find that friendship reduces opinion differences by 44 percent of the mean opinion gap. Our evidence supports a homophily-enforced mechanism: Friendships form among initially politically similar students, leading them to join political associations together, reinforcing their similarity.