6 degrees of separation? Try 6.6

The so-called 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.

For the purposes of the experiment, two people were considered to be acquaintances if they had sent one another a text message. The researchers looked at the minimum chain lengths it would take to connect 180 billion different pairs of users in the database. They found that the average length was 6.6 steps and that 78 percent of the pairs could be connected in seven hops or less.

Microsoft Messenger use is most intense in North America, Europe and Japan, and in the coastal regions of the rest of the world. While the study sample is huge, there is little way of knowing whether Microsoft Messenger users are as socially connected as the rest of humanity.

Why does it matter that people from around the world are closely tied together? Researchers said that the knowledge might have applications for political organizations, charity efforts, and missing-person searches.

“They could create large meshes of people who could be mobilized with the touch of a return key,” Horvitz said.