AddThis sharing tools are used on millions of domains, all over the world. As users interact with AddThis, anonymously across all of those domains, we are able to observe and determine their interest level in various types of content. We don't know who, specifically, these people are (the information is "non-personally identifying"), only that the person using that browser on that computer might like that particular topic.
By presenting this information, and how it is affected by things like sharing, we can help publishers understand what their most influential visitors care about, while still protecting their users' privacy. End-users can opt-out of this data collection at any time, ensuring that no information is collected about their anonymous interactions with AddThis sharing tools.
As this interest data is based on a large amount of anonymously aggregated data, you as a publisher will see more actionable data as your traffic levels increase.