Methods and apparatus to maintain audience privacy while determining viewing of video-on-demand programs

A method to monitor presentation of video-on-demand (VOD) media, the method comprising:

• obtaining subscriber metering data from a site metering device monitoring presentation of first VOD media at a first subscriber site;
• obtaining server metering data from a VOD server that is to provide VOD media including the first VOD media to a plurality of subscriber sites including the first subscriber site, the server metering data including first information associated with the first subscriber site, the first information indicating that the first VOD media has been provided to the first subscriber site, the first information being manipulated to preserve anonymity of the first subscriber site;
• obtaining, based on a metering device identifier associated with the subscriber metering data, a first media device identifier and first subscriber identification information, the first media device identifier identifying a first media device used to present the first VOD media at the first subscriber site, the first subscriber identification information identifying a first subscriber associated with the first subscriber site;
• and
• combining the first media device identifier and the first subscriber identification information to determine a first manipulated identifier to match a second manipulated identifier included in the server metering data to identify the first information associated with the first subscriber site.