Why Facebook’s Ad Buyers Are Not Happy Right Now

By: Michelle Toh for Fortune.

About a data discrepancy that stretched on for two years, according to a report.

Advertisers and media buyers are distressed after Facebookrevealed that it had been overestimating the average time users spent watching videos.

Facebook’s FB 0.11% error in reporting the metric was a result of only counting views of three seconds or longer when it calculated its “average duration of video viewed” metric, a Facebook employee explained in a post on thesite’s advertiser help center. Since it left out views that were shorter than three seconds, the average viewing time appeared higher than it actually was—a discrepancy that stretched on for two years, sources told The Wall Street Journal.

Facebook reported that it would be correcting the measure on its website about a month ago to factor in all video plays. It would also be renaming it from “average duration of video viewed” to “average watch time,” the company said.

Ad executives have since been asking the social media giant for more details, and expressed skepticism about the proposed solution.

See also: Instagram More Than Doubles Advertiser Base In Six Months

“Essentially, they’re coming up with new names for what they were meant to measure in the first place,” ad buying agency Publicis Media said in a memo informing its clients of the news.

The note said that Facebook had told the company that the estimated average viewing time was likely over-exaggerated by somewhere between 60% and 80%, according to theJournal.

Facebook released the following statement:

“We recently discovered an error in the way we calculate one of our video metrics. This error has been fixed, it did not impact billing, and we have notified our partners both through our product dashboards and via sales and publisher outreach. We also renamed the metric to make it clearer what we measure. This metric is one of many our partners use to assess their video campaigns.”

The announcement has raised questions about whether external companies should be brought in to measure analytics for advertisers.

“This once again illuminates the absolute need to have 3rd party tagging and verification on Facebook’s platform,” Publicis said.

“Seeing the Facebook news about overestimating video views for 2 years makes me wonder about Snapchat,”Shafqat Islam, co-founder of NewsCred wrote on Twitter. “Need 3rd party verification everywhere.”