  We present the results of a study of the Pinterest activity graph. Pinterest
is a relatively new and extremely popular content-based social network.
Building on a body of work showing that the hidden network whose edges are
actual interactions between users is more informative about social
relationships that the follower-following network, we study the activity graph
composed of links formed by liking, commenting, and repinning, and show that it
is very different from the follow network. We collect data about 14 million
pins, 7 million repins, 1.6 million likes, and several hundred thousand users
and report interesting results about social activity on Pinterest. In
particular, we discover that only 12.3% of a user's followers interact with
their pins, and over 70% of activity on each user's boards is done by
non-followers, but on average, followers who are active perform twice as many
actions as non-followers.
