Result: Motifs in co-authorship networks and their relation to the impact of scientific publications

Co-authorship networks, where the nodes are authors and a link indicates joint publications, are very helpful representations for studying the processes that shape the scientific community. At the same time, they are social networks with a large amount of data available and can thus serve as vehicles for analyzing social phenomena in general. Previous work on co-authorship networks concentrates on statistical properties on the scale of individual authors and individual publications within the network (e.g., citation distribution, degree distribution), on properties of the network as a whole (e.g., modularity, connectedness), or on the topological function of single authors (e.g., distance, betweenness). Here we show that the success of individual authors or publications depends unexpectedly strongly on an intermediate scale in co-authorship networks. For two large-scale data sets, CiteSeerX and DBLP, we analyze the correlation of (three- and four-node) network motifs with citation frequencies. We find that the average citation frequency of a group of authors depends on the motifs these authors form. In particular, a box motif (four authors forming a closed chain) has the highest average citation frequency per link. This result is robust across the two databases, across different ways of mapping the citation frequencies of publications onto the (uni-partite) co-authorship graph, and over time. We also relate this topological observation to the underlying social and socio-scientific processes that have been shaping the networks. We argue that the box motif may be an interesting category in a broad range of social and technical networks.