Abstract: A method performed by one or more computing devices. The method uses data identifying a plurality of users and a plurality of achievements. The data identifies which of the plurality of achievements each of the plurality of users has earned and when any such achievements were earned. The method includes ordering the plurality of achievements to define an ordered achievement list, and for each of the plurality of users, removing from the ordered achievement list any of the plurality of achievements identified in the data as having been earned by the user to define a recommended achievement list for the user. The method also includes identifying a selected achievement, and identifying as a set of similar users any of the plurality of users whose recommended achievement list includes the selected achievement.

Abstract: A method performed by one or more computing devices. The method uses data identifying a particular user of a plurality of users, a title, and a plurality of achievements that may be earned with respect to the title. The data identifying which of the achievements the particular user has earned. The method includes determining an achievement difficulty value for each of the achievements, determining a title interest contribution value for each of the achievements as a function of the achievement difficulty value determined for the achievement, identifying one or more of the achievements that were earned by the particular user, and determining a user interest value as a function of the title interest contribution value determined for each of the identified one or more of the achievements (earned by the particular user). The user interest value indicates a level of interest of the particular user with respect to the title.

Abstract: A method performed by one or more computing devices. The method uses data identifying a plurality of users and a plurality of achievements. The data identifies which of the plurality of achievements each of the plurality of users has earned and when any such achievements were earned. The method includes ordering the plurality of achievements to define an ordered achievement list, and for each of the plurality of users, removing from the ordered achievement list any of the plurality of achievements identified in the data as having been earned by the user to define a recommended achievement list for the user. The method also includes identifying a selected achievement, and identifying as a set of similar users any of the plurality of users whose recommended achievement list includes the selected achievement.