1. A method implemented by at least one processor, the method comprising: obtaining a message topic; processing a log of messages of users, wherein the processing comprises determining a portion of the messages in the log that are related to the message topic; and based on the processing, computing a topical impact score for an individual user, the topical impact score related to the message topic, wherein the topical impact score reflects: power of the individual user, the power indicating an amount of other users reached by the messages of the log that were sent by the individual user, and knowledge of the individual user, the knowledge indicating an extent to which the individual user is regarded as an authority on the message topic.
6. The method of claim 1 , wherein the processing further comprises: determining a power score indicating the power of the individual user; determining a knowledge score indicating the knowledge of the individual user, the knowledge score relating to the message topic; and computing the topical impact score as a product of the knowledge score and a log of the power score.