Friday, December 9, 2011

Only four degrees of separation, says Facebook

We are all a lot closer to Kevin Bacon than we thought.

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.

Sociologist Stanley Milgram, who tested the six degrees theory in the 1960s, found an average of 5.2 intermediate people in the US. At the time, he wrote that people at the end points were "not five persons apart, but 'five circles of acquaintances' apart." He thought of them as different "worlds" of acquaintances." Now, the Facebook team concludes, "people are in fact only four worlds apart."

The world just became a little smaller.

Hecht, Jeff. 2011. "Only four degrees of separation, says Facebook". New Scientist. Posted: November 22, 2011. Available online:

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