The Interactive Advertising Bureau (IAB) has again raised concerns about the measurement of web audiences and has called for major research groups to open up their systems to an independent audit.

IAB president and CEO Randall Rothenberg has written an open letter to the CEOs of comScore and Nielsen//NetRatings, challenging both firms to throw their methods open to scrutiny.

The IAB is seeking to put pressure on measurement groups over apparent discrepancies between their numbers and the internal figures of sites. 

Rothenburg said he objected to their use of representative panels to measure web audiences:

“To persist in using panels that potentially undercount or ignore the diverse populations that are the future of consumer marketing is to deny marketers the insights they need to build their businesses.

“We simply cannot let the internet, the most accountable medium ever invented, fall into the same bad customs that have hindered older media and angered advertisers for decades.”

The move also follows comScore’s introduction of a new ‘visits’ metric earlier this year, after complaints from Yahoo! that it was being penalised for its use of AJAX.

The stakes have also been raised for the measurement firm following its recent announcement of plans to list on the stock market.