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How does Facebook figure out who my friends should be?


I’ve subscribed to Facebook to see what it was all about, but used a
pseudonym instead of my real name, which is permitted, as I understand it. And
an alias of my email address being an unidentifiable number. I now receive
emails from Facebook listing people I might know. About half the people listed,
I do know and are in my address book on my computer. It can’t be a coincidence
that these people are listed. They would not recognize the pseudonym I use so
how does Facebook know that I know these people?

In this excerpt from
Answercast #30
, I look at some of the methods Facebook uses to find
associations between people, it’s not really anything to worry about.


Facebook’s friends suggestions

Facebook friend suggestions can seem really spooky.

I do know that they’re not going to go out and grab your address book unless you explicitly give it to them. There are some ways I know that they request access to some of your accounts, sometimes, but as long as you don’t do that, they won’t access your information.

Facebook methodology

Facebook does some amazingly intelligent stuff to infer who you know by what you do on Facebook.

For example, let’s say you have three friends: A, B, and C. I’ll give them generic names.

  • On Facebook, you go out and you friend A and B.

  • A and B happen to both know C.

  • So, because you’re friends with A and B, and because A and B both know C, it’s possible that Facebook says, “You know what, if these two friends of yours know this person, maybe you do too. So I’ll suggest them as a possible friend for you.”

The more complex your friends network gets, the more inferences Facebook can make. In fact, the better job it can do of figuring out who your friends might be.

  • You haven’t given it any additional information,

  • It hasn’t stolen any additional information from you,

  • It hasn’t even used (in your case) your real email address.

  • All it’s done is taken a look at who you have friended on Facebook.

Friend’s activity

Now, I say, “Friended.” It is my belief that Facebook is looking at more than just who you friend.

Particularly if you have the ability to see your friend’s activity without actually friending them on Facebook, it is possible that Facebook could notice that. That could be, from Facebook’s perspective, as good as being their friend.

In other words, Facebook might say:

  • You know what, you spend a lot of time looking at person A’s stuff,

  • And you spend a lot of time looking at person B’s stuff,

  • And they both know person C,

  • So, I’m thinking you might know person C as well.

And again if you have no friends, all you had to do was spend enough time looking at friend A’s stuff and friend B’s stuff and Facebook might be able to infer who your other friends might be.

Liking pages

Another approach is taking a look at what pages you like. For example, if you go to the Ask Leo! Fan Page, and like it, then all of a sudden that is a connection between you and all of the other fans of Ask Leo!

That by itself probably doesn’t mean a lot. But if you then go off and become a fan of another page, say, “This is True” or “Ask Dave Taylor,” or any of a number of other fan pages on Facebook, and a few of the other fans of Ask Leo! also happen to be fans of those other pages.

Facebook might start to think, “You know, you people all have a lot of common interests. Maybe you should get together; maybe you should know each other. In fact, maybe you do know each other, and I’ll suggest them as possible friends.”

Eerily accurate

So in general, people really get spooked sometimes by the friend suggestions that they see. They are spooked sometimes by how accurate they are.

In my opinion, there’s no need to be spooked at all.

Facebook is actually taking information that you’re giving it… and that information is your activity on Facebook. It’s using that information to try and figure out who you might know; who you might like to know; who you might share common interests with; and suggest them then as possible friends.

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4 comments on “How does Facebook figure out who my friends should be?”

  1. Facebooks friend suggestions are annoying, precisely because of Leo’s #1 suggestion.

    I am friends with my wife’s cousins, uncles, and aunts. We live in the east. My wife’s cousins, uncles, and aunts live in the west. So Facebook thinks that I want to be friends with all of my wife’s cousins, uncles, and aunts’ friends.

    And of course the more popular friend suggestions are the ones where I’m friends with my wife’s aunt, and cousin, and cousin’s children (think grandma, mother, children). Of course because those 5 people are all related and are friends with the gradma, or the cousin’s in-laws and church friends, Facebook assumes that I must want to be friends with those in-laws and church friends (whom I have never met in my life) because there are 5 friends in common.

    Facebook’s assumptions are flawed and I have more false positives because of it. It takes forever to weed out those people I don’t know to find suggestions of people I do know.

    I basically ignore the friend suggestions and just do a search for people that I am truly interested in. Why do I need 500 friends who I never have contact with?

  2. I understand the concept of Facebook’s correlation technique to produce friend suggestions but my experience would suggest something more devious – and a bit spooky.

    I became a friend of someone but after a month I cancelled both this friendship and my membership of FB. A few months later however FB sent me 3 friend suggestions. Two were known to me, were FB members, but were totally unknown to one another and had no friends and little interests in common. One lived in Devon and the other in Yorkshire. Indeed one friend had totally forgotten he was a member of FB and hadn’t used it for a number of years.

    The third friend suggestion was totally unknown to me and to the other 2.

    No correlation technique surely could have produced this friend suggestion. I simply do not trust FB.

    As I said, I believe that friend suggestions are much more complex than just who your friends are – your activity while logged in to Facebook and on Facebook (and possibly while on sites that have Facebook widgets installed) – is also data that can be used to determine the things and people that you might like. I certainly don’t consider it devious – most people simply don’t realize that massive amounts of data that are available for this kind of analysis. I can certainly understand, however, how the seemingly magical nature of some of the recommendations can lead to distrust.

  3. Even though I don’t let Facebook read my Outlook address book (or at least, not for several years) it’s possible that people I correspond with HAVE let FB access their address books, where it will find my email address. I suspect this is one source of some surprisingly accurate suggestions.

  4. There has to be something else going on here. I’m in social media management, so I have two FB accts. One for personal use and one for professional use. I ensure that there is no “connective tissue” between the two of them other than my birthdate. Neither of my accounts have access to any address books, GPS features of my devices, and I have gone through great pains to vette each friend to ensure there are no redundancies on either list. Now I work in city of over 3 million people and I encounter various acquantances on a daily basis, one of which is a hot dog vendor. Now this vendor does not have my email, or even know my last name (which would be useless as I use different pseudonyms on each acct and neither are searchable according to FB settings), we have a mutual friend on my personal account but we are not connected directly. This vendor has recently started a new FB acct and has only 3 friends currently, yet he with his own new pseudonym and a sparcely populated profile was suggested by facebook as a friend for my professional profile within hours of him setting up his acct. I am flabbergasted by the accuracy of the algorithim, but also spooked that FB can still identify one of my loose acquaintances with no personal information provided by either party. Weird!?


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