Facebook is overestimating its ad reach

Facebook ad metrics are facing scrutiny after it transpired the social network is overestimating the potential audience advertisers can expect to reach. A senior analyst from Pivotal Research Group points out that Facebook's Adverts Manager tool suggests demographic figures that exceed official numbers.

For example, advertisers are told that they could hit up to 41 million 18- to 24-year-olds in the US, but according to recent census data only 31 million 18- to 24-year-olds live in the US. The discrepancy is not isolated, as there are similar instances of inflated potential reach suggestions for various age groups in the US, UK and Canada.

Unsurprisingly, Facebook is defensive, saying that its figures are calculated differently to censuses. "Reach estimations are based on a number of factors, including Facebook user behaviors, user demographics, location data from devices, and other factors. 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."

This will come as little comfort to advertisers who have been told they could reach an audience that simply does not exist.

Over on Twitter, Jason Kint highlights a note from Pivotal Research Group's Brian Wieser that suggests the data put forward by Facebook is at odds with official census data:

Oomph. Pivotal analyst just dropped report showing Facebook Ad Manager claims 25 million more 18-34 year olds than the US census. pic.twitter.com/liLZz5rYx1

— Jason Kint (@jason_kint) September 6, 2017

Fortune experimented with the Adverts Manager tool and found the discrepancies to be present:

For advertisers trying to target Facebook users in the U.K., the company promises it could potentially reach 5.8 million 20-24 year-olds, 6.4 million 25-29 year-olds, and 5.2 million 30-34 year olds. When the last census was conducted in 2011, the U.K. only had 4.3 million 20-24 year-olds, 4.3 million 25-29 year-olds, and 4.1 million 30-34 year olds.

A cursory look at Facebook's claims for Canada, compared with census information, again showed major discrepancies—3.2 million claimed 20-24 year-olds versus the 2.2 million counted in reality, 3.4 million 25-29-year-olds versus 2.3 million, and so on.

It is possible for people on Facebook to report any age they like, so this could account for some of the discrepancies, but certainly not all of them.

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