Figure 6. (A) Histograms of the betweenness centrality (bc) normalized by total number of possible edges, [N*(N-1)]/2, where N is the number of authors, from all authors plotted in log scale. The majority of the authors have very small normalized bc (less than 0.005), and only a few authors have disproportionately large bc. (B) The averaged normalized bc over all authors having the same number of abstracts as a function of the number of abstracts. On average, the betweenness centrality of an author and the number of the abstracts follow a power law.