The researchers noted that Twitter relationships don’t have to be reciprocal — there’s no need to follow someone back who is following you, while Facebook relationships are two-way “friendships.” (Though that’s changing with the capability to “like” something.) Only 22.1 percent of Twitter user pairs follow each other, the researchers said. Moreover, they noted that most follower-followed relationships on Twitter are more akin to traditional-media relationships between subscribers to information and distributors of that information, with subscribers consuming information but having little contact with distributors. A relatively small number of users are the primary sources of news, with others redistributing that news; most tweets are related to timely topics; and retweets typically come very quickly — 35 percent in the first 10 minutes.
via niemanlab.org