Published online 13 March 2008 | Nature | doi:10.1038/news.2008.670


Six degrees of messaging

Study of instant messaging shows worldwide personal links.

How close are you to any other online chatter?Inspirestock

Yet more evidence has turned up to show that we are only six steps removed from almost anyone else on the planet.

Eric Horvitz, at Microsoft Research in Redmond, Washington, and Jure Leskovec, who was an intern at the time, crunched through masses of data, logging a month's worth of global 'instant messaging' conversations using Microsoft Messenger — software that facilitates chat, in a similar way to e-mail, but in a more instantaneous and less formal fashion. The researchers then counted how many messages were sent and from where: in total they tallied up a whopping 255 billion messages sent in the course of 30 billion conversations among 240 million people during June 2006.

No personal or identifiable data could be seen, and the researchers had no access to message content, although they could correlate messages with information about age and gender logged by users when they registered for the service. “We didn’t probe individuals,” says Horvitz, “we were looking at patterns.”

The resulting figures produced a neat map of communication hotspots across the world, and allowed Horvitz and Leskovec to trace the extent of separation between Microsoft Messenger users. They found that the average shortest number of jumps to get from one random user to another was 6.6; spookily close to the infamous six degrees of separation demonstrated practically in a group of 64 people by Stanley Milgram, at Harvard University, in the 1960s.

Horvitz says he was surprised that their analysis so closely matched the 1967 result. He wonders whether the number six is a basic constant for social interactions. “Do we have a natural harmonic for social communication?” he asks. “This is my conjecture — more work needs to be done on that.”

They will present their findings at the 17th International Conference on World Wide Web, in Beijing in April1.

Scaled up

In 2003 Duncan Watts, then at Columbia University and now at Yahoo! Research in New York, did a large email experiment that also confirmed the six degrees of separation idea2. His study involved 61,000 volunteers, compared to Leskovec and Horvitz’s 240-million sample. Watts is impressed that the trend that both he and Milgram saw has now been confirmed on such a large scale, and without having to set up a specific experiment: “They are using communication data, so the links do represent something real,” says Watts.

Horvitz and Leskovec saw a number of other trends in their data. Over long distances instant messenging between just two people, rather than groups, is more popular (the application allows up to 20 people to chat at once). People prefer to chat to the opposite sex, and tend to stick to talking with people in the same age group, especially when they are young.

Just for kids?

There are obvious biases in the data, with 15- to 30-year-olds being by far the biggest groups of users. Geographically, the majority of users were in North America, Europe and Japan; large areas of the developing world provided no data at all. In Africa, most users were located around coastal areas, and North Korea was completely 'dark'.


Adding to the analysis people from these 'dark' areas, and people who don't use computers, might be expected to produce a larger number for the shortest separation between people. But the team points out that there are other connections, such as those between grandchildren and grandparents that don’t show up in their map of instant messenger interactions.

It is difficult to say what would happen if the data truly covered the Earth's complete social network, but both Horvitz and Leskovec expect the numbers to stand up: “I can only speculate, but I think we would see something very similar, maybe a small increase in average path length,” says Leskovec, “something more towards seven degrees of separation.” 

  • References

    1. Leskovec, J. & Horvitz, E. Planetary-scale views on an instant-messaging network; available online at (2008).
    2. Dodds, P. S., Muhamad, R. & Watts, D. J. Science 301, 827-829 (2003).
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