Abstract: Effects of content communications propagated to users of a social networking system may be tracked and measured by the social networking system. Identifiers of content presented to a user within a time period prior to an action performed by the user are recorded in a first label object associated with the action. The action performed by the user generates new content to be presented to other users. The identifiers of the new content and the first label object are recorded in new label objects associated with actions performed by the other users subsequent to viewing the new content. Various metrics may be determined by analyzing the label objects associated with actions performed by users of the social networking system, including virality, reach, and identifying users that share a particular content item.