Emergence of Fractals in Social Networks: Analysis of Community Structure and Interaction Locality

Research on social network analysis (SNA) has been actively pursued. Most SNAs focus on either social relationship networks (e.g., Friendship and trust networks) or social interaction networks (e.g., Email and phone call networks). It is expected that the social relationship network and social interaction network of a group would be closely related to each other. For instance, people in the same community in a social relationship network are expected to communicate with each other more frequently than with people in different communities. To the best of our knowledge, however, there is not yet any empirical evidence to support the existence of such interaction locality in large-scale online social networks. This paper aims to bridge the evidence gap between intuition about interaction locality and confirmation that it occurs. We investigate the strength of interaction locality in large-scale social networks by analyzing several types of data: logs of mobile phone calls, email messages, and message exchanges in a social networking service. Our results show that strong interaction locality is observed equally in the three datasets and suggest that the strength of the interaction locality is fractal, by which we mean that the strength is invariant with regard to the scale of the community.