New Scientist tells us about Facebook’s analysis of the “friend” relationships in their social network. “Only four degrees of separation, says Facebook,” goes the New Scientist headline. Here’s their summary:

A few months ago, we reported that a Yahoo team planned to test the six degrees of separation theory on Facebook. Now, Facebook’s own data team has beat them to the punch, proving that most Facebook users are only separated by four degrees.

Facebook researchers pored through the records of all 721 million active users, who collectively have designated 69 billion "friendships" among them. The number of friends differs widely. Some users have designated only a single friend, probably the person who persuaded them to join Facebook. Others have accumulated thousands. The median is about 100.

To test the six degrees theory, the Facebook researchers systematically tested how many friend connections they needed to link any two users. Globally, they found a sharp peak at five hops, meaning that most pairs of Facebook users could be connected through four intermediate people also on Facebook (92 per cent). Paths were even shorter within a single country, typically involving only three other people, even in large countries such as the US.

“The world,” they conclude, “just became a little smaller.”

Well, maybe. There are a lot of things at play here, and it’s not simple. It is interesting, and it’s worth continuing to play with the data, but it’s not simple.

They’re studying a specific collection of people, who are already “connected” in a particular way: they use Facebook. That gives us a situation where part of the conclusion is built right into the study. To use the Kevin Bacon comparison, if we just look at movie actors, we’ll find closer connections to Mr Bacon than in the world at large. Perhaps within the community of movie actors, everyone’s within, say, four degrees of separation from Kevin Bacon. I don’t know any people in the movie industry directly, but I know people who do, so there’s two additional degrees to get to me. We can’t look at a particular community of people and generalize it to those outside that community.

There’s also a different model of “friends” on Facebook, compared with how acquaintance works in the real world. For some people, they’re similar, of course, but many Facebook users have lots of “friends” whom they don’t actually know. Sometimes they know them through Facebook or other online systems, and sometimes they don’t know them at all. Promiscuous “friending” might or might not be a bad thing, depending upon what one wants to use one’s Facebook identity for, but it skews studies like this, in any case.

People would play with similar things in the real-life “six degrees” game. Reading a book by my favourite author doesn’t count, but if I passed him on the street in New York City, does that qualify? What about if we went into the same building? If he held the door for me? If I went to his book signing, and he shook my hand and signed my copy of his book? Facebook puts a big e-wrinkle on that discussion.

But then, too, it’s clear that with blogs and tweets and social networking, we have changed the way we interconnect and interact, and we have changed how we look at being acquainted with people. I know people from the comments in these pages, and from my reading and commenting on other blogs. Yes, I definitely know them, and some to the point where I call them friends in the older, pre-social-network sense. But some I’ve never met face to face, nor talked with by voice.

So, yes, the world probably is “a little smaller” than it used to be. It didn’t just get that way suddenly, of course; it’s been moving in that direction for a while. Everything from telephones and airplanes to computers and the Internet have been taking us there.