There is an extremely large difference between the user demographic figures reported by Facebook itself (captured from their ad targeting system and aggregated by CPM Advisors), and those tracked via comScore’s Media Metrix online measurement panel. We should point out that the assumption that the Facebook figures are correct is by no means a foregone conclusion - especially as we report there is also a large lack of gender data available for older registered users. Also, the comScore Media Metrix figures are based on visitation estimates based on their October 2007 panel - they extrapolate the number of people from the US who visited Facebook.com whereas Facebook’s ad targeting system is based on data that consumers tell Facebook about themselves, and one would expect there to be a greater divergence in the numbers for less-frequent visitor groups. We do indeed see this, but the differences are still much larger than we expected. Also, we’d expect the registered user numbers to be an upper bound on the monthly visitor figures. Note that the weighted-average age of the audience targetable in the US via Facebook Ads according to their data currently is a bit over 22 years old.

Here is a breakdown on the Facebook vs. Comscore figures:

The largest difference then between the way comScore sees the Facebook audience and the reality thereof, is that instead of 13.6 million US people age 35 or older using Facebook, that number seems to be just 1.26 million — or less than 1/10th the size. For now, it seems that the Silicon Valley early adopters, journalists and others who have been riding the Facebook hype train need to face the facts that FB still is very much a college-age phenomenon. They are certainly pushing the envelope and driving innovation in many areas, but in no way is Facebook the mainstream application that some think.

Update: We are happy to share the underlying data in Excel format, just go to the contact page and let us know.