Six Clicks Of Separation

In a Web-connected world, even strangers are only a few electronic clicks away. A study finds that most anyone can reach a distant stranger in an average of six relays by asking friends and acquaintances to message some site seemingly closer to the target.

Researchers at Columbia University set up an experiment in which individuals would try to get a message to a stranger somewhere else in the world through the Internet. Participants knew basic facts about the 18 targets: name, location, profession and some educational background.

The participants were urged to send their contact message to someone they knew who was closer to the target. That person, in turn, was urged to send a message a contact that they knew. The process continued until the target received the message or, as often happened, the process broke down from the lack of interest.

More than 61,000 individuals from 166 countries signed up for the experiment and created a total of 24,163 message chains. Only 384 of the chains, however, reached their targets.

Most chains died, said Duncan J. Watts, a Columbia sociologist who led the study, due to fading of interest. Many messages were simply not relayed, cutting chains prematurely.

Of the chains that were completed, it took an average of four message relays, but Watts said "that is a misleading number because it is biased toward short chains." Longer chains, he said, are more likely to end due to lack of participating.

To compensate for this bias, he said, the researchers estimated how many messages would have to be relayed if there was perfect cooperation.

"That estimate is five to seven, with an average of six," he said. "That is the true answer and that is what the world actually looks like from the point of view of how the network is connected."

On average, said Watts, it would take five message relays for a searcher to find a target in the same country. When the target was in another country, it took, on average, an additional two messages.

Watts said that friends were most frequently used for relaying messages toward the target, but the most successful of the chains relied more heavily on professional contacts. That included sending messages to a target known only as someone in the same profession as the contact.

Also, Watts said that people who were only remote acquaintances played an important role in the successful chains. That's because close friends tend to know the same people and have the same contacts, while more distant acquaintances are more apt to bring in new contacts unknown to the searcher.

The experiment is now being repeated, with certain refinements, and Watts has posted an invitation for participants on the Web.

Watts said the experiment has a practical purpose.

"Networks can contain a lot of resources and if you learn how to navigate through them that can be a powerful tool for self advancement," he said. "The mechanisms people use to navigate networks are universal and this is a clean way to study that process and to find good strategies."