How does linkedin know who I know?

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How does linkedin know who I know?

Postby Diadem » Sun Jul 22, 2012 10:16 pm UTC

Today I signed up to linkedin, after having been pestered about it by friends for a while. During registration, it asked for access to my gmail contact list, but I refused this. I did however enter my real name, where I live, and also the university where I'm at. At this point, I have not entered any other personal information at all.

Yet somehow it's able to recommend dozens of people I know. How does it do that?

It turns out that three people actually used linkedin to send me an invite, so it makes sense that linkedin remembers those. And it could match a few people based on who those three people know, or based on my location. But it's also coming up with people I know in entirely unrelated ways, who live on the other side of the country.

Solely based on the information I provided, those links are simply impossible to get. So they must be mining other datasources. Facebook I guess. Though how it knows which facebook account is mine is a mystery, as there are several people with my name. Stranger is that it is recommending several people who I don't have on facebook, though they might be friends of friends. That would require incredibly advanced datamining on facebook though, to get that link.

Does anyone have a clue how they do it? I find it rather scary.
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Re: How does linkedin know who I know?

Postby Jacque » Sun Jul 22, 2012 10:35 pm UTC

Diadem wrote:advanced datamining
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Re: How does linkedin know who I know?

Postby Diadem » Mon Jul 23, 2012 2:32 pm UTC

Well, yeah. But how did it gain access to my facebook, let alone so many others? It really sounds like fishy things are going on here. Is facebook sharing this data without permission? I wouldn't put that above them, I guess.
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Re: How does linkedin know who I know?

Postby Chen » Mon Jul 23, 2012 2:35 pm UTC

Well what if THOSE people did give access to their gmail contact list? Wouldn't you be on that? Once it matches your email address with one it already has in its database it can suggest users to you based on who had YOU on their shared contact list.
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Re: How does linkedin know who I know?

Postby gorcee » Mon Jul 23, 2012 2:41 pm UTC

Chen wrote:Well what if THOSE people did give access to their gmail contact list?


Dingdingding. Basically that.
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Re: How does linkedin know who I know?

Postby Garm » Mon Jul 23, 2012 4:55 pm UTC

Here's a long (but very interesting, imo) article that provides a partial answer to your question: http://radar.oreilly.com/2012/07/data-jujitsu.html

tl;dr:
Jacque wrote:
Diadem wrote:advanced datamining


:D :D
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Re: How does linkedin know who I know?

Postby Izawwlgood » Mon Jul 23, 2012 5:12 pm UTC

Yeah, I've been a little weirded out on occasion by the power of this. People I communicated with over gmail once, 8 years ago, popping up on LinkedIn.
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Re: How does linkedin know who I know?

Postby ConMan » Mon Jul 23, 2012 11:34 pm UTC

I managed to be even more freaked out by Facebook's ability to do this. It suggested someone who (a) I have never contacted using the email that I provided to Facebook, (b) I have never contacted anyone who would associate with this person using the email that I provided to Facebook, (c) at the time, had not friended any of my friends or anyone I would be connected to this person via. My only guess was that it was done via mutual friends, but I didn't think there would be enough of them to push him to the top recommendation on my profile.
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Re: How does linkedin know who I know?

Postby Sheikh al-Majaneen » Tue Jul 24, 2012 4:04 am UTC

ConMan wrote:I managed to be even more freaked out by Facebook's ability to do this. It suggested someone who (a) I have never contacted using the email that I provided to Facebook, (b) I have never contacted anyone who would associate with this person using the email that I provided to Facebook, (c) at the time, had not friended any of my friends or anyone I would be connected to this person via. My only guess was that it was done via mutual friends, but I didn't think there would be enough of them to push him to the top recommendation on my profile.

On facebook I had had people showing up as friend suggestions who I posted on a forum with. We never emailed, they weren't in my list, I didn't share mine with them...creepy. Which is one of the reasons the previous sentence was in past tense.
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Re: How does linkedin know who I know?

Postby Ashlah » Tue Jul 24, 2012 4:07 am UTC

ConMan wrote:I managed to be even more freaked out by Facebook's ability to do this. It suggested someone who (a) I have never contacted using the email that I provided to Facebook, (b) I have never contacted anyone who would associate with this person using the email that I provided to Facebook, (c) at the time, had not friended any of my friends or anyone I would be connected to this person via. My only guess was that it was done via mutual friends, but I didn't think there would be enough of them to push him to the top recommendation on my profile.

I don't think you need more than one mutual friend for Facebook to make those suggestion. I've had plenty of suggestions with whom I have only one mutual friend.
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Re: How does linkedin know who I know?

Postby Adacore » Tue Jul 24, 2012 4:57 am UTC

The suggestions I see on Facebook are normally the closest friends to the people I've friended most recently, or people who have recently friended a number of my close friends. It clearly has an algorithm to determine which friends I currently associate with, and thus which of my friends' friends it should suggest. Also, sometimes, the more mutual friends you have with someone the lower they drop on the recommendation page, as I think Facebook demotes people that have been suggested but ignored quite harshly.

This does lead to weird situations where if I make friends with a couple (but don't know anyone else in their friendship circle), suddenly my entire suggestions list is dominated by their friends, who I don't know.
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Re: How does linkedin know who I know?

Postby K-R » Tue Jul 24, 2012 4:59 am UTC

Ashlah wrote:
ConMan wrote:I managed to be even more freaked out by Facebook's ability to do this. It suggested someone who (a) I have never contacted using the email that I provided to Facebook, (b) I have never contacted anyone who would associate with this person using the email that I provided to Facebook, (c) at the time, had not friended any of my friends or anyone I would be connected to this person via. My only guess was that it was done via mutual friends, but I didn't think there would be enough of them to push him to the top recommendation on my profile.

I don't think you need more than one mutual friend for Facebook to make those suggestion. I've had plenty of suggestions with whom I have only one mutual friend.

I often see suggestions with whom I have zero mutual friends. No idea who they are or why Facebook thinks I might know them.
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Re: How does linkedin know who I know?

Postby EdgarJPublius » Tue Jul 24, 2012 5:13 am UTC

Diadem wrote:Well, yeah. But how did it gain access to my facebook,


I dunno if you've been paying attention the last few years or not. But that's how facebook makes money.

Diadem wrote:. Is facebook sharing this data without permission?


You should really read the privacy policy sometime.
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Re: How does linkedin know who I know?

Postby ConMan » Tue Jul 24, 2012 5:51 am UTC

koberulz wrote:
Ashlah wrote:
ConMan wrote:I managed to be even more freaked out by Facebook's ability to do this. It suggested someone who (a) I have never contacted using the email that I provided to Facebook, (b) I have never contacted anyone who would associate with this person using the email that I provided to Facebook, (c) at the time, had not friended any of my friends or anyone I would be connected to this person via. My only guess was that it was done via mutual friends, but I didn't think there would be enough of them to push him to the top recommendation on my profile.

I don't think you need more than one mutual friend for Facebook to make those suggestion. I've had plenty of suggestions with whom I have only one mutual friend.

I often see suggestions with whom I have zero mutual friends. No idea who they are or why Facebook thinks I might know them.

As has been discussed, if you've given them access to your email contacts, and that person is in there, then they might suggest them - or if the other person has done so, and you're in *their* contacts - or, potentially (and this is where things get less certain), if some third party has done so, and both of you are in those contacts (or already friends with them).
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Re: How does linkedin know who I know?

Postby PatrickRsGhost » Tue Jul 24, 2012 10:37 am UTC

It's not just looking at e-mail contact lists. If you have entered other information in your profile (where you live, where you work, where you go/went to school, etc.), LinkedIn and Facebook look at those parameters and match them with other people who have the same data entered in those fields. It's basically one big fucking Data>Sort>Sort By>Column H>Column K>Column J>Column G>Column A for a huge-ass Excel spreadsheet.

It's more fun when you indicate you go to a large university/college, or work at some major, nationwide company.

For example, if you say you work at a nationwide retail chain, like Target, and only say "Target", it will look at all other people who say they also work at Target, even if it's not the same Target you work at. You could be working at the one in Conyers, Georgia, but even if you specified that you work at that specific Target location, the website's data-mining program will see "Target", and will suggest someone who works at a Target up in Tennessee, or over in Colorado, or Arizona, or New Mexico, or even up in North Dakota or Minnesota.

It could also be looking at the field or category Target falls under ("retail"), and end up suggesting people who work in the same or similar fields, and be employed at Wal-Mart, K-Mart, Sears, or perhaps something slightly more upscale, like Ross, Belk, Kohl's, or even some privately-owned small retail store found only in a handful of cities in a small area, like "Bobbie's Discount Boutique".

The point is, it looks at certain key words or phrases, and then like I said, does one big fucking Sort Data on a giant Excel spreadsheet.

I've had friends suggested for me on Facebook mainly due to there being x number of mutual friends between us, but I've also had people suggested because they either went or go to my old high school, lived or presently live in a city I used to live in, or live in now, or worked or presently work at a place I used to work at or work at now. Most of those that fall into either of those last two turn out to be younger than me. The "mutual friends" thing tends to be all over the map agewise.
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Re: How does linkedin know who I know?

Postby cjmcjmcjmcjm » Tue Jul 31, 2012 4:36 am UTC

I once found someone I suspect to be a one-time tutor of mine back from elementary school in the recommended friends list. The thing is, I haven't seen recommendations for other teachers of that school (of whom I'm sure at least a few others are on FB) nor do I believe I had her e-mail address. Assuming it is the right person (I don't remember her first name, and the last name is on a hunch), she's now an administrator at a liberal arts university.

LinkedIn, on the other hand, seemingly gave me random people from HS (fair enough, auto e-mail list checking) and the odd fellow student at my uni, but once those ran out, it was seemingly random. I was expecting more profs to be suggested as contacts.
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Re: How does linkedin know who I know?

Postby Menacing Spike » Wed Aug 01, 2012 4:03 am UTC

Garm wrote:Here's a long (but very interesting, imo) article that provides a partial answer to your question: http://radar.oreilly.com/2012/07/data-jujitsu.html


welp it's more than partial

it doesn't explain anything about the algorithm at all

Also from my experience, it recommends people that worked in the same institutions that I had a lot of email contact with. Since I didn't give linkedin my email, it seems it is from theirs, as many people in the thread pointed out.
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Re: How does linkedin know who I know?

Postby Garm » Wed Aug 01, 2012 4:40 pm UTC

It's true, the article doesn't talk about the algorithm but it does give some insight to their thinking and possible sources of connection.

As an aside, I don't think that something like LinkedIn is handled by SQL. It's a Big Data problem so they're probably using something more advanced.
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Re: How does linkedin know who I know?

Postby Jacque » Wed Aug 01, 2012 9:32 pm UTC

Menacing Spike wrote:it doesn't explain anything about the algorithm at all

That's the secret sauce. You don't get that recipe out of a cookbook.

Garm wrote:As an aside, I don't think that something like LinkedIn is handled by SQL. It's a Big Data problem so they're probably using something more advanced.

NoSQL and Hadoop (plus a bunch of other crap I'm sure).
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