Self-organization leads to hierarchical modularity in an internet community

Many naturally-occurring networks share topological characteristics such as scale-free connectivity and a modular organization. It has recently been suggested that a hierarchically modular organization may be another such ubiquitous characteristic. In this paper we introduce a coherence metric for the quantification of structural modularity, and use this metric to demonstrate that a self-organized social network derived from Internet Relay Chat (IRC) channel interactions exhibits measurable hierarchical modularity, reflecting an underlying hierarchical neighbourhood structure in the social network.