Three more advertising trade groups have echoed the demand that Nielsen/NetRatings and comScore metric systems be audited, reports ClickZ.

A statement issued by the American Association of Advertising Agencies, Association of National Advertisers and Advertising Research Foundation made the request, following the Interactive Advertising Bureau's call for independent auditing.

The groups seek to ensure the methodologies employed by the measurement firms are sound, and that subsequent numbers provide value to organization members.

Nielsen has agreed to begin a full Media Ratings Council accreditation process. comScore consented to a one-time audit, which could take about six months to complete.