Exposure hypothesis and its variations.

<p>The probability of retweeting as a function of the number of followees who have tweeted a post, (A) averaged over all users, (B) by breaking down users into classes based on the number of following friends they have, (C) by breaking down users into classes based on the betweenness in their ego networks, and (D) by breaking down users into classes based on the clustering coefficient in their ego networks. Medians of betweenness and clustering coefficient are used as cut-points for grouping users.