Figure 2

Stochastic block model and group polarization for the collaboration network in the field of inequalities in health. (See Supplementary Figs. S3-S9 for all other fields). (A) Collaboration network and best fit of the hierarchical stochastic block model (hSBM). Each node in the network represents a prominent researcher, and each edge represents a different collaboration (coauthored paper) between a pair of researchers. Prominent researchers in North America and Europe are represented as circles and triangles, respectively. Different colors correspond to the groups identified by the hSBM, so that nodes with the same color have a similar collaboration pattern with other researchers and therefore fulfill a similar structural role in the collaboration network. Node size represents the betweenness centrality of the researcher in the network. We omit the names of the researchers so as not to distract from the patterns we aim to explore; for reproducibility, we provide the names of the prominent researchers in Supplementary Fig. S2, and in Supplementary Figs. S3-S9 for the other fields. (B) Block model of the collaboration network. Each node represents a group of researchers with similar collaboration patterns (that is, a different color in (A)), with node size representing the number of researchers in the group. The width of the edges represents the number of collaborations between groups, and loops represent collaborations within each group. The color of each node indicates the fraction of researchers in the group that are based in North America, so that dark blue nodes represent groups with mostly Europe-based researchers, and red nodes represent groups with mostly North America-based researchers. (C) We define the polarization of a group as the number of same-continent researchers in the group over the random expectation for such number (Methods). The vertical line indicates the mean group polarization for the observed collaboration network. We randomize authors’ affiliations and calculate the distribution of expected (null) polarization values. The empirical value is well above the null expectation, so that the group structure of the observed network is significantly polarized