1. A computer-implemented method comprising: identifying a first topic group of users of a social networking system that have expressed an affinity for a page of the social networking system that corresponds to a first topic; determining, for a category, that the category includes the first topic and a plurality of other topics; identifying a category group of users of the social networking system that have expressed an affinity for a page corresponding to at least one of the topics included in the category; identifying a plurality of candidate pages of the social networking system, each candidate page having a corresponding candidate topic about which users of the first topic group and users of the category group can have differing opinions; for each candidate page of the plurality of candidate pages of a social networking system: computing a user interest measure quantifying an amount of interest expressed by users of the first topic group for the candidate topic corresponding to the candidate page, computing a category interest measure quantifying an amount of interest expressed by users of the category group for the candidate topic corresponding to the candidate page, and computing a divergence measure between the first topic group and the category group based on the user interest measure and the category interest measure; generating, for the first topic, a first topic profile based on the divergence measures; and storing the first topic profile.