Distribution in social networks refers to the pattern of connectivity between nodes. It is not unreasonable to assume that, especially as overall network size becomes larger, the likelihood that every node in the network will be directly connected to every other node becomes that much smaller. Similarly, it is reasonable to assume that the patterns of disparate connections throughout larger networks will appear more and more irregular. Researchers are interested in discovering what we can learn about collective action from analyzing these patterns. The concepts covered in this article include bridges, structural holes, and centrality. The related notion of distance is the subject of its own article, later in the series.
Bridges are connections between sets of nodes (subnetworks) within a network that would otherwise not be connected to each other, or that would be connected through such a long path that the nodes might not even be aware that the connection exists. A simple example would be the case of friendship groups among high school students. A group of students in grade nine is not likely to share friends in common with a group of students in grade twelve. However, if one of the students in the grade nine group was the younger sibling of one of the students in the grade twelve group, then that sibling relationship would form a bridge between the two groups.
Sociologist Ronald Burt suggested that bridges in social networks could be viewed as spanning structural holes, basically empty spaces in the network topology. Empirical research has demonstrated that managers who constitute nodes at the ends of bridges within organizational networks tend to have earlier access to information, are exposed to alternate viewpoints, have the opportunity to act as gatekeepers, and, as a consequence, have greater career success. Burt has suggested that filling structural holes is a means of building social capital. Extending these ideas to the market, identifying and filling structural holes provides the ideal opportunity for entrepreneurship.
Centrality refers to the extent to which a particular node plays a central role in a network. It is measured in three ways. Degree centrality is a measure of the number of nodes that are linked to a focal node. Closeness centrality describes how short the paths are between a focal node and all of the other nodes in a network. Betweenness centrality measures the shortest path between any two nodes in the network that pass through the focal node.
Recent research by information scientists has shown that social science disciplines play a much greater role in knowledge communication and interaction among disciplines that do disciplines in the so-called hard sciences. Based on co-citation analysis of aggregated journal articles, the findings demonstrated that social science disciplines have a greater number of ties to other disciplines (degree). They are more directly linked to a wider range of other disciplines (closeness), and they are more likely to act as a bridge between disciplines (betweenness). Interestingly, journals in the field of public administration demonstrated the greatest centrality.