From the The Ad Contrarian:
For years anyone with a brain has known that Facebook "metrics" are a joke. They make shit up, imbeciles at agencies believe it, dimwit clients fund it, and - bingo - more ad money. Most famously, not long ago they inflated video viewing time on their site by as much as 80%. […]
According to Brian Wieser of Pivotal Research Group, one of the industry's most respected media analysts, Facebook is at it again.
Facebook's Ads Manager says that the website is capable of reaching 41 million Americans between the ages of 18 and 24. The problem is there are only 31 million Americans of that age. But hey, what's 10 million people here or there?
You have to admire Facebook for their ability to reach 10 million imaginary 18-24 year olds. But as well as they do against imaginary 18-24 year olds, where they really excel is against non-existent 25-34 year olds. They reach 60 million of them. Unfortunately, there are only 45 million alive.