Facebook has admitted that over a two-year time period, it overestimated the amount of time people spent on the site watching videos. “We recently discovered an error in the way we calculate one of our video metrics,” the company said in a statement. "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." One ad buying firm, Publicis Media, told The Wall Street Journal that the social media behemoth overestimated the amount by between 60 and 80 percent, calling the problem “unacceptable.” Knowing how popular videos are is critical for advertisers to know what works and what doesn’t. Traffic metrics also drive ad pricings. According to the newspaper, a new metric is being introduced to correct the problem. The problem stemmed from what Facebook called the “average duration of video viewed,” which sounds self-explanatory, but the social media giant was not counting views of fewer than three seconds. This drastically inflated the numbers. Facebook has said it fixed the issue, but Publicis says the problem shows the need for third-party verification of Facebook metrics.