An example method includes facilitating installation of a data collector on a media device; collecting, via the data collector, a media identifier indicative of media presented at the media device; encrypting a user identifier that identifies the user of the media device, the encrypting of the user identifier based on a first encryption key corresponding to a first database proprietor having first user information associated with the user identifier; encrypting a device identifier that identifies the media device, the encrypting of the device identifier based on a second encryption key corresponding to a second database proprietor having second user information associated with the device identifier; sending the media identifier to a data collection server; sending the encrypted user identifier to a second server associated with the first database proprietor; and sending the encrypted device identifier to a third server associated with the second database proprietor.