Facebook seems to think it can advertise to more U.S. millennials than actually exist

Facebook is promising advertisers that it can reach 25 million more American millennials than the Census believes to exist.

The social network boasts that ads on its platform will be seen by up to 41 million people in the United States between the ages of 18 and 24 and 60 million 25-to-34-year-olds. But as Pivotal analyst Brian Wieser pointed out in a research note this week, the U.S. Census Bureau's data indicates only 31 million and 45 million of each respective group even live in the country.

The discrepancy would be nowhere near the first time Facebook has been caught misrepresenting its metrics to advertisers. The company first had to apologize last fall after a bombshell report revealed that it had been artificially inflating view numbers for video ads. That revelation was followed by a string of reports on other bugs, mistakes, and misrepresentations that amped up tensions between the platform and its wary advertisers.

A Facebook spokesperson said in a statement that its estimated reach is based on "a number of factors" and "not designed to match population or Census estimates.

"Reach estimations are based on a number of factors, including Facebook user behaviors, user demographics, location data from devices, and other factors," the company said in a statement. "They are designed to estimate how many people in a given area are eligible to see an ad a business might run. They are not designed to match population or census estimates. We are always working to improve our estimates."

Facebook global sales chief Carolyn Everson also expanded on that defense in an interview with Business Insider. She stood by the social network's numbers and argues that press reports treating the difference as a metrics error are misleading.

"It’s not like it’s some bug," Everson told the site. "Our estimates are not meant to match census data."

If Facebook is miscalculating, it would mark probably its most blatant metrics blunder yet given how easy it is to fact-check and debunk. That made for some easy jokes on Twitter:

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Since Facebook only knows as much about its users' ages as they are willing to submit on their profile, there's bound to be some margin of error. Unlike the Census, Facebook also accounts for travelers in an area temporarily. But the discrepancy seems to be awfully large to attribute only to those factors.

Still, Facebook's projected reach figures don't affect how the company bills businesses, and they're generally not the most important consideration for most advertisers.

Then again, maybe it's the Census that is miscounting here.

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