Big data isn’t an entirely new concept: We have an entire division of the U.S. government dedicated to quantifying our nation’s population, and the Census Bureau has been doing so in its current form since 1902. The scope, quantity, and granularity of the data has changed, though, and Facebook in particular specializes now in knowing pretty much everything about everyone. But someone is clearly wrong, because the two have population estimates that just don’t match.

One analyst has recently noticed a fairly big discrepancy, Reuters reports: Facebook is promising users that simply shouldn’t exist.

The discrepancy

Facebook tells advertisers that they can reach up to 41 million users in the 18-24 age bracket. At first blush, that seems to make perfect sense. Pretty much everyone has Facebook, after all; the company boasts 236 million monthly active users in the U.S. and Canada, and they tend to skew younger.

Except, the analyst notes, the U.S. Census Bureau currently says that there are 31 million people in the country in that age bracket. The gap between accepted federal reality and Facebook reality also persists in the next age bracket up, users ages 25-34, he notes.

So who’s right?

On the one hand, the Census Bureau has decades of experience coming up with scientifically accurate population estimates based on birth and death rates, immigration rates, representative surveys, and even literally going door to door and counting people. They have specialized in gathering this data for quite some time, and accuracy is important when basically every federal decision (and no small number of state ones) rests on your data.

But there’s some wiggle room in there. Estimates are just that: Data-based, educated guesses and models that may not exactly match reality no matter how hard you try.

On the other hand, Facebook data is both specific and granular. Users provide their birthdays, and Facebook captures where you log in from. So the company knows if you’re inside the boundaries of the U.S., and it knows how old you are.

But there are caveats aplenty, even as creepy as Facebook’s all-knowing eye can be. Every profile that Facebook says exists doubtless actually exists, but they may not be what they seem to be.

Plenty of people, for example, have more than one Facebook profile. Plenty of people can and do lie about their age. And plenty of Facebook accounts purporting to be 18-34-year-old women are spambots. So Facebook’s hard data isn’t infallible.

Facebook agreed to Reuters in a statement that its audience estimates don’t match census data, but said that’s not only fine, but intentional, as the ad reach numbers “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.”

But if the people don’t exist, can even Facebook actually reach them? That, apparently, is a philosophical question for our digital, big-data era.

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