1. A method for selecting a subset of keywords from a set of master keywords in user profiles of social network users, comprising: sending invitations to a first group of users of a social networking system and to a second group of users of a social networking system; observing responses to the invitations from the first and second groups of users; computing a first histogram of each keyword in the master keywords based on the occurrence of the keywords in a first group of user profiles, the first group of user profiles associated with the first group of users; computing a second histogram of each keyword in the master keywords based on the occurrence of the keywords in a second group of user profiles, the second group of user profiles associated with the second group of users; computing, by a computing system, a score based on a comparison of the first histogram and the second histogram for each keyword in the master keywords, wherein computing the score for each keyword comprises computing a difference between an information gain for an entry in the first histogram corresponding to the keyword and an information gain for an entry in the second histogram corresponding to each keyword; ranking the master keywords based on the score of the keywords; and selecting a subset of keywords from the master keywords based on the ranking.