One of LinkedIn’s strengths is its “how you’re connected” feature, which shows how you’re linked to second degree contacts. Seeing who you have in common with someone helps you understand who they are, what they’re like, and whether it’s worth getting to know them. It’s often more informative than the blurbs people write about themselves.

“Any friend of Joe’s is a friend of mine”

But this LinkedIn feature is becoming less useful due to an insidious form of network pollution. Like coastal erosion, this network pollution is a slow process that’s barely noticeable from one day to the next, but could be hugely damaging in the longer term. And I think I know who’s responsible for this network pollution – recruiters.

Before I continue, I should say that this isn’t an anti-recruiter rant. Recruiters may be responsible for this network pollution, but the blame lies with LinkedIn, and I’ll talk more about this later. Building a big contact list is essential to a recruiter’s job and they can’t be expected not to do this. But this is what’s weakening the value of LinkedIn’s “how you’re connected” feature, and quite possibly its network as a whole.

If you’re a LinkedIn user, you’re not just a person – you’re a “node”, which is a fancy way of saying that you can connect people to one another. If one of your contacts finds another one of your contacts on LinkedIn, you will be the node that connects them. And as a connecting node, your usefulness comes from the quality of your relationships with those two individuals. If the person searching knows that you’re picky about who you connect with (which you clearly are, only highly discerning people read this blog after all), your connection to that person is itself a notable endorsement.

If you were Marlo, you’d probably be more interested in people you knew through Prop Joe than through McNulty

Not every “node” on LinkedIn is as discerning and useful as you are, though. Some nodes are far more promiscuous, connecting to lots of people they’ve never met, let alone worked with, and the more promiscuous someone is the less useful they become as a LinkedIn node. This is where recruiters come in. They hoover up connections, which means that you often find your second degree contacts are connected to you through recruiters. But as connecting nodes, the recruiters aren’t all that useful because they’re not very choosy about who they connect with.

Bubbles pollutes Marlo’s network because he knows so many people. Now everyone’s a second degree contact

OK, maybe I’m stretching the analogy by comparing Bubbles to a recruiter, so I’ll drop it now. The general principle is that, if you’re connected to more than a couple of recruiters, searching LinkedIn will turn up more and more people who are second degree contacts, but that you only know through recruiters. The value of someone being a second degree contact slowly declines, because when a recruiter is the common contact you learn nothing more meaningful than that you both once looked for a job, or once tried to hire people.

It’s like sharing a mild dislike of rain – common ground, yes, but not very meaningful. This is what I mean by “network pollution”. The value or interestingness of the network is dropping because of recruiters and other “super-nodes” who are turning nearly everybody into your second degree contacts.

LinkedIn isn’t the only service susceptible to this kind of network pollution. Twitter will sometimes recommend another user to you because you have a “follow” in common. And if that “follow” is, say, your best friend, that’s good grounds for a recommendation. But if the common follow is Stephen Fry, Barack Obama, or any other celebrity account with millions of followers, that’s pretty useless. If Last.fm recommended someone to you because you both listened to the Beatles, that would be pretty useless too (which is why music recommendation algorithms are hard to get right). All social networks have to deal with problems like this where “super-nodes” undermine the value of recommendations based on shared connections.

So as I said earlier, this is a LinkedIn issue and not the fault of recruiters who are simply trying to do their jobs. Recruiters will continue to add connections, other people will continue to accept them, and the usefulness of “how you’re connected” will continue to drop. It’s not a very serious problem right now, but LinkedIn needs to think of how it can design for this aspect of its social graph, which is something it seems to take pretty seriously – and rightly so

And for now the best kind of advise from me: start reading more tips from professionals on problem you are trying to solve.