1. A computer-implemented method comprising: identifying a 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; identifying a category that 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; for each page of a plurality of pages of a social networking system, each page having a corresponding topic: computing a user interest measure quantifying an amount of interest expressed by users of the topic group in the topic corresponding to the page, computing a category interest measure quantifying an amount of interest expressed by users of the category group in the topic corresponding to the page, and computing a divergence measure based on the user interest measure and the category interest measure; generating, for the first topic, a topic profile based on the divergence measures; and storing the topic profile.