  Scholars, advertisers and political activists see massive online social
networks as a representation of social interactions that can be used to study
the propagation of ideas, social bond dynamics and viral marketing, among
others. But the linked structures of social networks do not reveal actual
interactions among people. Scarcity of attention and the daily rythms of life
and work makes people default to interacting with those few that matter and
that reciprocate their attention. A study of social interactions within Twitter
reveals that the driver of usage is a sparse and hidden network of connections
underlying the declared set of friends and followers.

Computers and Society;Physics and Society