Answering the Interactive Advertising Bureau’s call for an independent audit of the respective audience methodologies of comScore and Nielsen/NetRatings, the two companies say they are currently at various stages of finalizing such a process. In separate open letters, both organizations expressed a willingness to have a dialog with IAB and seemed to concede the need for increased transparency and accuracy, as demanded by Randall Rothenberg, IAB’s president and CEO. In a letter issued last Friday, he called for both to submit their measurement models to the Media Ratings Council for accreditation.

In the case of comScore, the company says its methodology and processes is currently in the final stages of a review by the Advertising Research Foundation. It will release the findings “in the near future.” Rothenberg’s critique of comScore zeroed in on its use of panels to serve as representations of larger populations. ComScore promised to get to the bottom of the disparity between panels and website server logs. ComScore Release

As for Rothenberg’s request that they both submit to a review by the MRC, William Pulver, the CEO of Nielsen/NetRatings, writes that the company is the only internet audience measurement research company to have completed the MRC’s pre-audit, and is currently executing on a formal research plan jointly developed with the MRC’s Research Committee. Pulver also insists that the company is going beyond the IAB’s suggestions, noting that aside from working to integrate panel and website site data, NNR also vows to quickly develop a “proper measurement of streaming media and AJAX.” It is also working with sibling Nielsen Media Research on synthesizing TV and online data. NNR Open Letter (PDF)

Update: Rothenberg said the IAB is “pleased that Nielsen//Netratings and comScore have agreed publicly to seek an audit by the Media Rating Council and, in Nielsen’s case, full MRC accreditation. This shows a commitment to true accountability and to the transparency necessary to assure advertisers, agencies, and media that their investments are sound.  We’re also pleased by their willingness to work with the IAB to assure the continued solidity of their measurement processes as interactive media evolve. However, we should point out that these companies have been promising the IAB and MRC that they’d undertake audits for several years, and they still haven’t taken place. We challenge them to set - and stick with - a timetable.”

• — IAB Calls For Audits Of comScore And Nielsen/NetRatings Measurement Methods