Emergence of Structural Inequalities in Scientific Citation Networks

Structural inequalities persist in society, conferring systematic advantages to one group of people, for example, by giving them substantially more influence and opportunities than others. Using bibliometric data about authors of scientific publications from six different disciplines, we first present evidence for the existence of two types of citation inequalities. First, female authors, who represent a minority in each discipline, receive less recognition for their work relative to male authors; second, authors affiliated with top-ranked institutions, who are also a minority in each discipline, receive substantially more recognition compared to other authors. We then present a dynamic model of the growth of directed citation networks and show that such systematic disparities in citations can arise from individual preferences to cite authors in the same group (homophily) or the other group (heterophily), highly cited or active authors (preferential attachment), as well as the size of the group and how frequently new authors join. We analyze the model theoretically and show that its predictions align well with real-world observations. Our theoretical and empirical analysis sheds light on potential strategies to mitigate structural inequalities in science. In particular, we find that merely making group sizes equal does little to narrow the disparities. Instead, reducing the homophily of each group, frequently adding new authors to a research field while providing them an accessible platform among existing, established authors, together with balanced group sizes can have the largest impact on reducing inequality. Our work highlights additional complexities of mitigating structural disparities stemming from asymmetric relations (e.g., directed citations) compared to symmetric relations (e.g., collaborations).