1. A method comprising: receiving a media identifier and an impression identifier from a media device, the media identifier being indicative of media presented at the media device; receiving the impression identifier in association with first user information from a first database proprietor as a result of the first database proprietor obtaining a first identifier sent from the media device, the first identifier identifying at least one of the media device or a user of the media device; receiving the impression identifier in association with second user information from a second database proprietor as a result of the second database proprietor obtaining a second identifier sent from the media device, the second identifier identifying at least one of the media device or the user of the media device; identifying the first user information and the second user information as associated with a same user based on the impression identifier; and associating the first user information and the second user information with the media identifier.