Evolution of interdependent co-authorship and citation networks

Studies of bibliographic data suggest a strong correlation between the growth of citation networks and their corresponding co-authorship networks. We explore the interdependence between evolving citation and co-authorship networks focused on the publications, by Indian authors, in American Physical Society journals between 1970 and 2013. We record interactions between each possible pair of authors in two ways: first, by tracing the change in citations, they exchanged and, second, by tracing the shortest path between authors in the co-authorship network. We create these data for every year of the period of our analysis. We use probability methods to quantify the correlation between citations and shortest paths, and the effect on the dynamics of the citation-co-authorship system. We find that author pairs who have a co-authorship distance d <= 3 significantly affect each other's citations, but that this effect falls off rapidly for longer distances in the co-authorship network. The exchange of citation between pairs with d = 1 exhibits a sudden increase at the time of first co-authorship events and decays thereafter, indicating an ageing effect in collaboration. This behaviour suggests that the dynamics of the co-authorship network appear to be driving those of the citation network rather than vice versa. Moreover, the majority of citations received by most authors are due to reciprocal citations from current, or past, coauthors. We conclude that, in order to answer questions on the nature and dynamics of scientific collaboration, it is necessary to study both co-authorship and citation network simultaneously.