Instant-Messagers Really Are About Six Degrees from Kevin Bacon

By Peter Whoriskey
Washington Post Staff Writer
Saturday, August 2, 2008

Turns out, it is a small world.

The "small world theory," embodied in the old saw that there are just "six degrees of separation" between any two strangers on Earth, has been largely corroborated by a massive study of electronic communication.

With records of 30 billion electronic conversations among 180 million people from around the world, researchers have concluded that any two people on average are distanced by just 6.6 degrees of separation, meaning that they could be linked by a string of seven or fewer acquaintances.

The database covered all of the Microsoft Messenger instant-messaging network in June 2006, or roughly half the world's instant-messaging traffic at that time, researchers said.

"To me, it was pretty shocking. What we're seeing suggests there may be a social connectivity constant for humanity," said Eric Horvitz, a Microsoft researcher who conducted the study with colleague Jure Leskovec. "People have had this suspicion that we are really close. But we are showing on a very large scale that this idea goes beyond folklore."

In recent years, the massive databases yielded by cell phone records have been exploited by researchers to better understand human movements and social networks. Stripped of text messages and personally identifiable information, the records indicate users' location and patterns of contact.

The Microsoft research focused on the popular concept that has inspired games such as Six Degrees of Kevin Bacon and a well-known play by John Guare. A "degree of separation" is a measure of social distance between people. You are one degree away from everyone you know, two degrees away from everyone they know, and so on.

But proof of the theory has been thin.

Its origins lie in the work done in the '60s by Stanley Milgram and Jeffrey Travers. In an oft-cited 1969 work, they put the figure at 6.2, though they never referred to it as "degrees of separation."

Their finding was based on asking 296 people in Nebraska and Boston to send a letter through acquaintances to a Boston stockbroker.

The subjects were told to send the letter to an acquaintance who could best advance the letter to the target, but most failed: Only 64 of the original 296 letters reached the stockbroker. Of those letter chains that were complete, the average number of degrees of separation was 6.2. The high failure rate, and the possibility that the incomplete chains reflected much more distant relationships, led some to question the results. Also, all of the subjects were in the United States. What would happen if the test was expanded to the planet?

The idea was taken up again, this time on a global scale, by Columbia University researchers in a 2003 report of an e-mail experiment. More than 24,163 volunteers agreed to try to send an e-mail through acquaintances to one of 18 target persons in 13 countries. Only 384 of those 24,163 letter chains were completed. Of those completed chains, the average number of steps was 4, and using statistical techniques, the researchers estimated that the average length in all of the chains was between five and seven steps. Still, it was an estimate.

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