Three Degrees of Distance on Twitter
  Recent work has found that the propagation of behaviors and sentiments through networks extends in ranges up to 2 to 4 degrees of distance. The regularity with which the same observation is found in dissimilar phenomena has been associated with friction in the propagation process and the instability of link structure that emerges in the dynamic of social networks. We study a contagious behavior, the practice of retweeting, in a setting where neither of those restrictions is present and still found the same result. 
Jorge Fabrega, Pablo Paredes
cs.SI physics.soc-ph