Homophily in Collaborations among US House Representatives, 1981 -- 2018

Effective lawmaking requires collaboration among legislators, who form coalitions to advance their legislative agendas. In the US House of Representatives, these collaborations develop in a context of shifting political party control. In this paper we explore how legislators' party and gender identities simultaneously influence whom they choose as collaborators by examining differential party and gender homophily during a period of shifting party control and increasing representation of women. We introduce new methods for inferring legislative collaboration networks from bill co-sponsorship data, then estimate cross-sectional logistic regression models on these networks from 1981 -- 2015. We find evidence of differential homophily by both party and gender: Republicans and women tend to prefer same-party and same-gender political collaborators more than Democrats and men. However, party homophily (i.e. partisanship) is stronger than gender homophily, suggesting that party is a more salient identity for legislators than gender.