Issues in Identifying Structurally important Nodes in Networks
Friday, November 21, 2003 - 11:00am - 11:50am
Stephen Borgatti (Boston College)
This paper considers the problem of identifying sets of structurally important nodes in a network. A number of related issues are considered. First, I outline the different reasons why we might want to identify key nodes, showing that different measures (known as centrality measures in the social network literature) are needed for each. Second, I show how structural importance is affected by the manner in which things flow through a network. A typology is constructed to classify types of flows in terms of the kinds of trajectories that are possible (e.g., paths, trails or walks) and whether transmission occurs via serial replication, parallel replication or transfer. The relative importance of nodes in a given graph changes depending on what kind of flow process is operating. Third, I consider the problem of measuring the importance of sets of nodes. Finally, the subtext of the paper is a commentary on the nature of centrality measures and what they are intended to measure.