1. A method, comprising: identifying, by one or more processors, a user in a community; determining, by the one or more processors and for each particular topic of a plurality of topics: communications that have been distributed from the user to other users in the community and that belong to the particular topic, and wherein the particular topic has only a subset of all communications distributed from the user; determining, by the one or more processors, a first reach of the communications that relate to the particular topic, wherein the first reach represents a first quantity of users who received the communications; determining, by the one or more processors, other communications that relate to the particular topic that have been distributed from a first set of users in the community to a second set of users that is different from the first set of users in the community for the particular topic, wherein the first set of users does not include the user; determining, by the one or more processors, a second reach of the other communications that relate to the particular topic; determining, by the one or more processors, an influence score to be associated with the user for the particular topic, the determination based on comparing the first reach to the second reach, wherein the second reach represents a second quantity of users who received the other communications; storing, by the one or more processors, the influence score for the particular topic in association with the user; and determining, by the one or more processors and based on the influence score associated with the user, that the user is an expert with respect to at least one of the particular topics.