  Social media allow for an unprecedented amount of interaction between people
online. A fundamental aspect of human social behavior, however, is the tendency
of people to associate themselves with like-minded individuals, forming
homogeneous social circles both online and offline. In this work, we apply a
new model that allows us to distinguish between social ties of varying
strength, and to observe evidence of homophily with regards to politics, music,
health, residential sector & year in college, within the online and offline
social network of 74 college students. We present a multiplex network approach
to social tie strength, here applied to mobile communication data - calls, text
messages, and co-location, allowing us to dimensionally identify relationships
by considering the number of communication channels utilized between students.
We find that strong social ties are characterized by maximal use of
communication channels, while weak ties by minimal use. We are able to identify
75% of close friendships, 90% of weaker ties, and 90% of Facebook friendships
as compared to reported ground truth. We then show that stronger ties exhibit
greater profile similarity than weaker ones. Apart from high homogeneity in
social circles with respect to political and health aspects, we observe strong
homophily driven by music, residential sector and year in college. Despite
Facebook friendship being highly dependent on residence and year, exposure to
less homogeneous content can be found in the online rather than the offline
social circles of students, most notably in political and music aspects.
