Advertisers on Facebook can target users based on pages they follow. The Russians targeted more than 700 different interests, such as Texas secession and Bernie Sanders.

To aggregate these specific interests into broad groups, we used an algorithm to cluster them based on the number of times different interests were targeted by the same ad.

For example, ads about gun rights often targeted people interested in Guns & Ammo as well as National Rifle Association, so the algorithm placed them in the same group. We then named the groups based on the topics they targeted.

Since these aggregate groups come from the way ads were originally targeted, they sometimes contain anomalous interests. For example, Libertarianism in ads targeted at left-wing interests and Christianity in ads targeted at right-wing interests.