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Understanding Community Structure for Large Networks

Franke, B; (2016) Understanding Community Structure for Large Networks. Doctoral thesis , UCL (University College London). Green open access

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Abstract

The general theme of this thesis is to improve our understanding of community structure for large networks. A scientific challenge across fields (e.g., neuroscience, genetics, and social science) is to understand what drives the interactions between nodes in a network. One of the fundamental concepts in this context is community structure: the tendency of nodes to connect based on similar characteristics. Network models where a single parameter per node governs the propensity of connection are popular in practice. They frequently arise as null models that indicate a lack of community structure, since they cannot readily describe networks whose aggregate links behave in a block-like manner. We generalize such a model called the degree-based model to a flexible, nonparametric class of network models, covering weighted, multi-edge, and power-law networks, and provide limit theorems that describe their asymptotic properties. We establish a theoretical foundation for modularity: a well-known measure for the strength of community structure and derive its asymptotic properties under the assumption of a lack of community structure (formalized by the class of degree-based models described above). This enables us to assess how informative covariates are for the network interactions. Modularity is intuitive and practically effective but until now has lacked a sound theoretical basis. We derive modularity from first principles, and give it a formal statistical interpretation. Moreover, by acknowledging that different community assignments may explain different aspects of a network’s observed structure, we extend the applicability of modularity beyond its typical use to find a single “best” community assignment. We develop from our theoretical results a methodology to quantify network community structure. After validating it using several benchmark examples, we investigate a multi-edge network of corporate email interactions. Here, we demonstrate that our method can identify those covariates that are informative and therefore improves our understanding of the network.

Type: Thesis (Doctoral)
Title: Understanding Community Structure for Large Networks
Event: University College London
Open access status: An open access version is available from UCL Discovery
Language: English
Keywords: Central limit theorems, degree-based network models, network community structure, nonparametric statistics, statistical network analysis
UCL classification: UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
URI: http://discovery.ucl.ac.uk/id/eprint/1531993
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