Stability and dynamics of communities on online question–answer sites

Abstract

Social networks are present in our everyday lives, not just in face to face communication, but also when we communicate through the Internet. The latter leaves massive traces of data and thereby opens opportunities to acquire a better understanding of social communities in general. In this work, we are particularly interested in the patterns of volunteer efforts within the communities. To that end, we examine the community structure of several large online question–answer sites and how they evolve over time. To describe the user interaction patterns concisely, we employ the hyperbolic community model. This statistical model allows for a summary of each community in each time step by means of intuitive parameters that reflect the connectivity pattern within the network. Our study of the temporal evolution of these parameters reveals an important characteristic: In contrast to what has been observed earlier in the analyses of growth behaviour of online communities, we observe that the user activity within a community is constant with respect to its size throughout its lifetime. Furthermore, the structural organisation of different communities across different question–answer sites seems to follow a common scheme: There is a small group of users who is responsible for the majority of the social interactions.