Study revives six degrees theory

Instant messaging has become part of everyday life for millions

A US study of instant messaging suggests the theory that it takes only six steps to link everyone may be right - though seven seems more accurate.

Microsoft researchers studied the addresses of 30bn instant messages sent during a single month in 2006.

Any two people on average are linked by seven or fewer acquaintances, they say.

The theory of six degrees of separation has long captured people's imagination - notably inspiring a popular 1993 film - but had recently seemed discredited.

One of the researchers on the Microsoft Messenger project, Eric Horvitz, said he had been shocked by the results.

"What we're seeing suggests there may be a social connectivity constant for humanity," he was quoted as saying by the Washington Post newspaper.

"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."

Urban myth?

The database used by Mr Horvitz and his colleague Jure Leskovec covered all of the Microsoft Messenger instant-messaging network, or roughly half of the world's instant-messaging traffic, in June 2006.

For the purposes of the study, two people were considered to be acquaintances if they had sent one another an instant message.

Examining the minimum chain lengths it would take to connect all the users in the database, they found the average length was 6.6 steps and that 78% of the pairs could be connected in seven links or fewer.

The idea of six degrees of separation was conceived by US academic Stanley Milgram, after experiments in which he asked people to pass a letter only to others they knew by name.

The aim was to get it, eventually, to a named person they did not know living in another city.

The average number of times it was passed on, he said, was six - hence, the six degrees of separation.

However, in July 2006, Judith Kleinfeld, professor of psychology at Alaska Fairbanks University, went back to Milgram's original research notes and discovered that 95% of the letters sent out had failed to reach their target.

She suggested that the six degrees theory might be the academic equivalent of an urban myth.

The Microsoft researchers said that, to their knowledge, their study had for the first time validated Milgram's theory on a planetary scale.

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