Both Nielsen/NetRatings and comScore have responded to the head of the Interactive Advertising Bureau's call that they allow themselves to be audited by the Media Ratings Council, reports AdAge.

In response to IAB chief Randall Rothenberg's open letter, both Nielsen and comScore have made statements showing how they are working on becoming more transparent with their numbers. NetRatings' CEO William Pulver says his firm has already completed a "pre-audit" by the MRC and that full accreditation should be coming soon.

comScore says it has allowed the Advertising Research Foundation to evaluate its numbers and methodology and will be releasing those results soon. The statement from the company says it is confident it can stand up to third-party evaluation.