Facebook's eerie accuracy of guessing people I know.

August 25, 2014

Once, a long time ago (I was still young and foolish ;-) I made a Facebook page. I made one connection, with a person abroad. Some time later I deleted the account. And completely forgot about it. Short story, happy end. Or not...

Some time ago I needed to check something on Facebook that required me to have an account. It turned out that my previously deleted account was not deleted at all, but merely deactivated. So without thinking I signed in again, thus reactivating the account. Maybe I should not have done that... Because since that day I receive daily emails from Facebook encouraging me to connect to people Facebook thinks I may know. And it is eerily good at guessing some people I may know!

Like I said, I only have one Facebook connection with a person abroad. So of course Facebook thinks that I must somehow know all friends of that friend. Clearly, I don't. However, every once in a while it comes up with a few Dutch people, that I indeed all know. Like today the list included a friend of a friend, a sensei of the style of karate I try to practice, and a remote friend that I see once every few months and that I used to play music with a few years ago. A few weeks ago it suggested a former student of mine, and my bassoon teacher.

I wonder how Facebook determines these guesses. The suggestions are not people that themselves requested to connect to me on Faceboook (I just checked). The friend of a friend is also a friend of another friend (are you still with me ;-) that sent me a connection request. So that may explain it. But the others I cannot easily explain. The sensei certainly does not know me. I have never published the name of my student or my bassoon teacher. Trying to find a link between us using Google doesn't return a match. So where those came from I don't know.

Interestingly enough Facebook never suggests people that are really close to me (like my wife, the friend whose friend Facebook does suggest, or my own karate sensei). Makes you wonder whether Facebook wouldn't be a great tool for law enforcement and intelligence agencies to find acquaintances of 'people of interest'.

In case you spot any errors on this page, please notify me!
Or, leave a comment.
, 2014-08-25 12:35:40

There is an option in Facebook to let it retrieve the contacts from your e-mail account. If someone who has you on their contact list has ever done it - there you are!

Hans de Zwart
, 2014-08-25 13:15:36

Hey Jaap-Henk, LinkedIn has the same capabities… I am quite sure that is has to do with the fact that both services do their utmost best to capture whole address books. Their mobile apps have made this endlessly easier for them. LinkedIn keeps on asking if I want to ‘make my experience’ better by allowing them to show which of my contacts use LinkedIn too and aren’t connected with me yet.

Imagine the kind of inferences you would be able to make if you had everybody’s address book. I am sure there only is a one- or two-step connection from the sensei to you right?

, 2014-08-25 14:54:06

Interestingly enough, there is a two step link from that sensei to me (through my own sensei). However, I am quite certain I am not on my sensei’s contact list. It is similarly unlikely that me and that student could be linked through contact lists.

Someone suggested on twitter that maybe the algorithm is to select people that are both on someone else’s contact list as possible friends. However that algorithm would create a lot of noise (many people on my own contact list don’t know each other at all). If you would add the requirement that possible friends should at least both be a member of at least x contact lists of other people, the noise would disappear. But then probably the mactehs Facebook would find are people that probably know each other very well (they are in a clique). Like I wrote in the blog, Facebook only fiends my acquaintances, not my close friends…