Abstract: A cluster of users that share a common trait may be useful to a social networking system for various purposes, such as targeting advertising. Users of a social networking system are added to a cluster based on information about each user, which may include declared profile information, user history, and/or social information. The system initially adds users to a cluster based on a selected attribute and then verifies the accuracy of the cluster by sending a poll to a subset of the users in the cluster. The poll questions test whether the users are accurately in the cluster. The system may infer a specific life event, such as a recent engagement, from other information indicative of the life event, such as messages from a user's connections related to the engagement. The system then uses the poll to verify whether the inference is accurate.