In an open letter to comScore and Nielsen//NetRatings, officials at the Interactive Advertising Bureau have called upon both firms to submit to third-party audits of their internet measurement methods.

"The goal of the IAB and the entire interactive industry is simple: to achieve transparency in audience counts and to revise out of date methodologies," the letter read.

The letter asked that both firms submit to audits by the Media Rating Council (MRC).

In October, comScore CEO Magid Abraham said his company had submitted to a pre-audit by the MRC, but pointed out that full audit would unnecessarily slow comScore's ability to adapt and innovate.

"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," IAB President Randall Rothenberg said. "And it certainly appears to us as if these audiences are being undercounted or disregarded."

Officials from both Nielsen and comScore did not return a request for comment on the IAB letter at post time.