Facebook exaggerated a key metric advertisers use to assess the performance of their videos on the platform by potentially as much as 80% for more than two years, The Wall Street Journal reported on Thursday. 
 
 It's an embarrassing screwup, and the report suggests one ad buyer, Publicis Media, was "upset" by the error. But while it certainly looks bad, there are a few reasons it why probably won't be as bad for Facebook as it seems. 
 
 The company acknowledged in a post on its Advertiser Help Center website that its metric for average video viewing time had been inflated because it didn't include video views lasting under three seconds. Facebook added that it was introducing a fix to provide a more accurate metric to include all views: "Average Watch Time." 
 
 A Facebook representative told Business Insider: "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." 
 
 Why this isn't as bad as it looks 
 
 Average video view time is just one metric Facebook offers advertisers to assess the impact of their videos. Many marketers look at total views or the view completion rate to determine whether their videos were a success. 
 
 Crucially, average video view time isn't what Facebook calls a "billable event." Facebook doesn't charge for video ads that were viewed for less than three seconds, unless advertisers actively choose to be charged on this basis. You can't bid on "average view time." 
 
 So many marketers may have simply assumed — as advertising executives including Anheuser-Busch InBev senior director of digital connections Azania Andrews and Laundry Service CEO Jason Stein have pointed out on Twitter — that people who watched a video for less than three seconds (therefore users they didn't pay to reach) were not included in the average view time metric anyway. 
 
 Why it's still pretty bad 
 
 Regardless, it's still not a good look for Facebook. It continues the narrative that Facebook is a black box that doesn't expose its inner workings to the people who fund its very existence. 
 
 Sir Martin Sorrell, the CEO of the world's biggest advertising group, WPP, which spent $1 billion of its clients' marketing budgets on Facebook last year, has called Facebook out on this before. He has previously said Facebook's three-second video viewability threshold was "ludicrous" and on several occasions has called for Facebook to offer better independent measurement tools. 
 
 He told Business Insider on Thursday: "That's why we invested in comScore and built a media measurement business in over 50 countries around the world. We have also been calling for a long time for media owners like Facebook and Google not to mark their own homework and release data to comScore to enable independent evaluation. The referee and player cannot be the same person." 
 
 Keith Weed, the chief marketing officer at the consumer-goods giant Unilever, said in an interview last year that without online media giants offering third-party verification, "It's like letting them mark their own homework." 
 
 In its defense, Facebook has formed a partnership with the third-party analytics firm Moat to provide data on how its Facebook video ads are performing — a move that Weed in a Facebook press release said was "very encouraging." The company has since opened up its platform to other video-measurement partners, including Integral Ad Science, Nielsen, and comScore. Marketers can request this data, though it doesn't come as standard. 
 
 While some people might argue that, regardless, many agencies may have been using Facebook's average video view data to encourage marketers to spend on Facebook's video ads, it's up to marketers to be savvy and use all the data available to them — particularly independent, third-party data — to determine whether those ads are performing well. 
 
 After this article was first published on Friday, Facebook's vice president of advertising and global operations, published this statement in an attempt to clarify the issue: 

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 Facebook miscalculated the average time viewers spent watching videos on its site, drawing fire from big ad buyers and marketers. WSJ's Sarah Rabil joins Lunch Break with Tanya Rivero and explains how the miscalculation happened and the financial impact on both Facebook and its advertisers. Photo: AP 
 
 Big ad buyers and marketers are upset with Facebook Inc. after learning the tech giant vastly overestimated average viewing time for video ads on its platform for two years, according to people familiar with the situation. 
 
 Several weeks ago, Facebook disclosed in a post on its “Advertiser Help Center” that its metric for the average time users spent watching videos was artificially inflated because it was only factoring in video views of more than three seconds. The company said it was introducing a new metric to fix the problem. 
 
 Some ad agency executives who were also informed by Facebook about the change started digging deeper, prompting Facebook to give them a more detailed account, one of the people familiar with the situation said. 
 
 Ad buying agency Publicis Media was told by Facebook that the earlier counting method likely overestimated average time spent watching videos by between 60% and 80%, according to a late August letter Publicis Media sent to clients that was reviewed by The Wall Street Journal. 
 
 A spokeswoman for Publicis Media, a division of Publicis Groupe SA, referred calls to Facebook. Publicis was responsible for purchasing roughly $77 billion in ads on behalf of marketers around the world in 2015, according to estimates from research firm Recma. 
 
 GroupM, the ad buying unit of WPP PLC, also was notified of the discrepancy by Facebook, another person familiar with the matter said. 
 
 On Friday, Facebook apologized. “The metric should have reflected the total time spent watching a video divided by the total number of people who played the video. But it didn’t,” said David Fischer, vice president of business and marketing partnerships, in a Facebook post. “While this is only one of the many metrics marketers look at, we take any mistake seriously.” 
 
 Facebook had said in an earlier statement: “We recently discovered an error in the way we calculate one of our video metrics.” It added: “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 news is an embarrassment for Facebook, which has been touting the rapid growth of video consumption across its platform in recent years. 
 
 Due to the miscalculated data, marketers may have misjudged the performance of video advertising they have purchased from Facebook over the past two years. It also may have impacted their decisions about how much to spend on Facebook video versus other video ad sellers such as Google’s YouTube, Twitter, and even TV networks. 
 
 Media companies and publishers are affected, too, since they’ve been given inaccurate data about the consumption of their video content across the social network. Many use that information to help determine the types of content they post. 
 
 For the past two years Facebook only counted video views of more than three seconds when calculating its “Average Duration of Video Viewed” metric. Video views of under three seconds were not factored in, thereby inflating the average. Facebook’s new metric, “Average Watch Time,” will reflect video views of any duration. That will replace the earlier metric. 
 
 In its note to clients, Publicis said the change was an attempt to obfuscate Facebook’s earlier miscalculations. 
 
 “In an effort to distance themselves from the incorrect metrics, Facebook is deprecating [the old metrics] and introducing ‘new’ metrics in September. Essentially, they’re coming up with new names for what they were meant to measure in the first place,” the memo said. 
 
 The miscounting could also fuel concerns among advertisers and media companies about the so-called “walled gardens” that companies including Facebook and Google are often described as operating. Both companies keep a tight grip on data, and only allow limited third-party tracking firms to plug into their systems. 
 
 Keith Weed, chief marketing officer of Unilever, said in an interview last year, tech companies that don’t let third parties measure their platforms is equivalent to “letting them mark their own homework.” 
 
 The Publicis note said, “This once again illuminates the absolute need to have 3rd party tagging and verification on Facebook’s platform. Two years of reporting inflated performance numbers is unacceptable.” 
 
 —Shalini Ramachandran contributed to this article. 
 
 Write to Suzanne Vranica at suzanne.vranica@wsj.com and Jack Marshall at Jack.Marshall@wsj.com
– Anyone poking around on Facebook's "Advertiser Help Center" a few weeks ago may have stumbled across a post that's now getting a lot more publicity: Facebook has been overestimating average viewing time for videos on the site, likely between 60% to 80% and for two years, the Wall Street Journal reports by way of a memo ad-buying agency Publicis Media sent to clients. Facebook has since released a statement: "We recently discovered an error in the way we calculate one of our video metrics," though it adds the "discrepancy" has been remedied and didn't affect billing. Facebook has been at the forefront of pushing video, and these boosted metrics may have influenced marketers' buying decisions, leading them to choose Facebook over competitors like YouTube (owned by Google) or even TV networks. What caused the error: Facebook only counted views that were more than three seconds, upping the average viewing time. Facebook says it's now renamed the metric to "make it clearer what we measure"—changing "Average Duration of Video Viewed" to "Average Watch Time"—but Publicis isn't buying it. "Essentially, they're coming up with new names for what they were meant to measure in the first place," the memo reads. But while Business Insider acknowledges the news is bad, it also says it "isn't as bad as it looks," noting average video viewing time is just one of many metrics provided and advertisers aren't charged for videos viewed for less than three seconds.