Analysis of Ego Network Structure in Online Social Networks

Results about offline social networks demonstrated that the social relationships that an individual (ego) maintains with other people (alters) can be organised into different groups according to the ego network model. In this model the ego can be seen as the centre of a series of layers of increasing size. Social relationships between ego and alters in layers close to ego are stronger than those belonging to more external layers. Online Social Networks are becoming a fundamental medium for humans to manage their social life, however the structure of ego networks in these virtual environments has not been investigated yet. In this work we contribute to fill this gap by analysing a large data set of Facebook relationships. We filter the data to obtain the frequency of contact of the relationships, and we check - by using different clustering techniques - whether structures similar to those found in offline social networks can be observed. The results show a strikingly similarity between the social structures in offline and Online Social Networks. In particular, the social relationships in Facebook share three of the most important features highlighted in offline ego networks: (i) they appear to be organised in four hierarchical layers; (ii) the sizes of the layers follow a scaling factor near to three; and (iii) the number of active social relationships is close to the well-known Dunbar's number. These results strongly suggest that, even if the ways to communicate and to maintain social relationships are changing due to the diffusion of Online Social Networks, the way people organise their social relationships seems to remain unaltered.