1. A method, comprising: determining, by executing an instruction with a processor of an audience measurement entity, whether a first request includes a first cookie, the first request identifying media provided to a client device; when the first request does not include the first cookie, generating the first cookie by executing an instruction with the processor of the audience measurement entity; sending, from the processor of the audience measurement entity, a response to the first request, the response including an identification of the first cookie used by the audience measurement entity and an indication of a database proprietor; receiving, by executing an instruction with the processor of the audience measurement entity, a mapping of the first cookie to a second cookie used by the database proprietor and demographic information associated with the second cookie by the database proprietor; and associating, by executing an instruction with the processor of the audience measurement entity, the second cookie and the demographic information with an impression of the media.