The Interactive Advertising Bureau (IAB) has announced it has reached an agreement with both comScore and Nielsen/NetRatings over auditing of their measurement techniques.

Last month, the IAB challenged both metrics firms to throw open their methods to inspection by independent auditors and expressed concern about the use of panels to measure web audiences.

Both firms have now agreed to auditing, according to the IAB:

“Nielsen//NetRatings has formally announced its entrance into a full audit and accreditation process with the Media Rating Council, and comScore is in the final stages of its pre-audit with the MRC and indicated a commitment to finalising the timeline for a full audit and accreditation within the next 90 days.”

As well as criticising panel-based measurement, the IAB had also raised concerns about discrepancies in audience measurements of media companies and the metrics firms.

Media firms have often queried the firm’s measurements, as they generally produce lower visitor figures than in-house server logs, though some of this discrepancy could be attributable to cookie deletion.