When Facebook last year announced it had misstated key engagement metrics in regard to video views, it drew attention to a problem that had been dogging the ad industry for a while: the fact that Facebook’s numbers weren’t independently audited.

Last month, however, Facebook agreed to audits by the Media Rating Council. Soon afterward, Google announced it was expanding its MRC accreditation to YouTube videos.

Both of those decisions, which open up so-called walled gardens to outside scrutiny, earned broad applause from members of the Association of National Advertisers. According to a survey, 89 percent of its 113 members surveyed saw the development as positive.

But ANA isn’t taking the positive developments on the ad audit front lying down. Last week, the group announced that it was calling on Amazon, Foursquare, Instagram, LinkedIn, Pinterest, Snapchat, and Twitter to follow suit. These firms have not announced or previously undergone such audits as of yet.

“In an era of concerns about transparency in the advertising supply chain, independent audits of the large digital enterprises by the MRC are very positive developments,” the association stated in a report last week. “Furthermore, it’s clear from the ANA survey that there is overwhelming support from client-side marketers for independent audits by the Media Rating Council.”

In comments on the endeavor to Ad Age, ANA Group Executive Vice President Bill Duggan said that such walled gardens create problems for advertisers.

“One frustration of marketers is they are unable to optimize if walled gardens don’t open up and share data,“ Duggan explained.

At least one company, Pinterest, said it was already moving toward working with MRC, though the effort has taken a back seat to other projects. A spokesperson told Ad Age that the company was “committed to third-party measurement.”

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