Update: AdNews has updated the original article with the latest rebased estimates from the ABS as well as adding new figures from Nielsen. The headline figure changes from 2 million to 1.7 million and all subsequent calculations have been adjusted.
Facebook claims its platform allows advertisers to reach 1.7 million more 15- to 39-year-old users in Australia than the country's official population.
The gap between Facebook users and population data has been revised from the original article AdNews ran last week to incorporate the latest rebased estimates of 2016 census data. This includes adjusting undercounts and overcounts of younger and older demographics as well as adding 600,000 residents who were overeas on census day and not included in the ABS's original estimate.
It provides a more accurate picture of the difference between Australia's official population and the number of users Facebook says advertisers can reach in this market.
The gap is signficant when compared to the size of Australia's largest cities. The additional 1.7 million users on Facebook in the millennial and Gen X age groups are nearly enough to populate Australia's fourth-largest city, Perth.
Such a sizeable gap raises questions about how Facebook calculates its audience, what this is made up of and whether advertisers and media buyers should rely solely on Facebook's figures when planning mass reach campaigns on the platform.
Although ABS population data does not account for fluctuations in short-term visitors that Facebook would include, it is statistically unlikely these would amount to an additional 1.7 million 15 to 39 year olds in a country of 24 million people.
It's important to note that the two sets of data measure different things. ABS data counts the number of people who live in Australia while Facebook's audience refers to the number of users on its platform that it calculates are geographically located in Australia.
Facebook tells AdNews there are several factors that determine its audience reach that need to be considered and its user audience is not a like-for-like comparison with population.
“Reach estimations are based on a number of factors, including Facebook user behaviors, user demographics, location data from devices and other factors," Facebook told AdNews.
"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.”
AdNews ran tests on Facebook's audience tool to see how its reach varied across age groups and whether this correlates to population data. A consistent pattern across large population areas the Facebook’s user audience exceeded population data in younger demographics and was well below among older generations.
The largest difference between Facebook's user audience and population data was in the 20s. Facebook calculates it has 1.2 million more users than the 3.5 million recorded in the 2016 census, which includes 138% more 20-24s and 129% more 25-29s.
This falls to 377,650 more users in their 30s before Australia's population overtakes Facebook’s audience by 362,552 for people in their 40s with the gap widening to 966,359 in the 50s.
There was a similar trend when comparing Nielsen figures. In 15-24s, Facebook’s counted 1.16 million more, in 25-34s the difference was 977,000 and in 35-44s the gap drops to 300,000. Interestingly, Nielsen estimates 1.5 million more 55-plus users than Facebook estimates.
AdNews investigated possible reasons why Facebook's audience reach is so different to official census data.
Short-term visitor figures show that there were 1.67 million more than departures than arrivals in 2016. That means more people left the country for holidays, business trips or other reasons than arrived, although the figures are likely to fluctuate between seasons and school holiday periods.
Bucking the overall trend are 20 to 29 year-olds, which had 167,000 net arrivals throughout the year. This means that Facebook’s audience figures could receive seasonal boosts among its largest user group, although this would never account for a 1.7 million difference in population.
A theory put forward by marketing strategy consultant Simon Kemp is that a proportion of Facebook users maybe lying about their age, particularly younger users who want to appear of a legal age in their country, while older users may understate to appear more youthful.
In an analysis piece, Kemp also notes that there could be "a number of fake profiles created for click farm purposes by unscrupulous third-parties".
Kemp says these anomalies are unlikely to be caused by a glitch in Facebook's system or the result of Facebook intentionally trying to deceive marketers. He advises marketers not to solely rely on age demographic targeting when using the platform.
Facebook says its data quality is regularly measured by independent third parties and "is found to be highly accurate". It says that advertisers concerned with the accuracy of Facebook's demographic targeting can have Nielsen independently verify it.
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