9. The computer-implemented method of claim 8 , further comprising: computing a first topic affinity score for a first user not in the topic group by applying the topic profile to information of the social networking system about the first user; and predicting, based on the first topic affinity score, that the first user has an affinity for the first topic.
11. The computer-implemented method of claim 9 , wherein the topic profile comprises identifiers of ones of the plurality of object and the corresponding divergence measures, and wherein computing the first topic affinity score comprises: computing, for each object in the profile, a value based on the divergence measure for the object and based on whether the first user has expressed an affinity for the object; and computing a sum of the values.