This is an ARF Research Review of the Media  MetrixMethodology as developed by comScore,
Inc. (comScore). The purpose of this review is two fold:
1. To review the objectives, design, methodology and validation of the comScore Media Metrix panel service.
2. To render an opinion of the adequacy of the design, methodology, and validation to meet the stated objectives, both in theory and in

practice, insofar as the practice has been represented to the ARF by comScore. This review is based solely on the assertions

and representations of comScore and is not an ARF audit.