Six Degrees Apart

Stanley Milgram, a social psychologist, designed a very clever experiment towards the end of the 1960s to test this 'small' world theory. Milgram and his research assistant, Jeffrey Travers, handed out 300 letters to various people in the cities of Boston and Omaha. They were instructed to hand them to a single individual , a stockbroker in Sharon, Masschetsus. To do this the subjects had to send the letter by mail to a friend who they thought was closer to the target individual than they were. The friend was given the exact same instructions and so Milgram set up a chain of go-betweens. To his surprise Milgram found that the average length of the chains created in this way, was approximately six. This was the average for those of the 300 chains were actually completed (64).

Since Milgram's time, the small-world conundrum has become a phenomenon within society. This has been particularly noticeable since John Guare, the playwright, used the catchy phrase "Six Degrees of Separation" as the title of his 1990 play.

Since Stanley Milgram first proposed the idea of "six degrees of separation" other sociological experiments have been conducted. Because Milgram's experiment was fairly small its results have been questioned by some sociologists. Peter Sheridan Dodds and his colleagues at Columbia University conducted a modern version of the Milgram study via the Internet. They recruited some 60,000 people from around 166 different countries to participate in the experiment.

The study volunteers were given the identity of an end user participant, one of 18 located around the world. They were then instructed to send an e-mail to someone they thought would be able to get the message nearer to the end user. It appears that the high participant numbers were necessary for this world wide experiment because just 384 e-mail chains, or three percent actually found their way to the end users email inbox. The average length of a completed chain comprised four people. This was described as an artificially low figure because the longer the chain, the less likely it was for the original email to find its intended destination. By factoring in the rate of dropouts, researchers were able to calculate a median chain length of between five and seven people.

In addition to strengthening the six-degrees of separation theory, the Columbia University study found that successful message transmission did not rely on HUB individuals with unusually high numbers of acquaintances as was previously thought to be the case.

Related Links:
Watts, D.J., Dodds, P.S., and Newman, M.E.J. Identity and search in social networks. Science, 296, 1302-1305 (2002).

Guare, J. Six Degrees of Separation: A Play. (Vintage Books, New York, 1990).

Watts, D.J. and Strogatz, S.H. Collective dynamics of 'small-world' networks. Nature 393, 440-442 (1998).

Pool, I. de Sola and Kochen, M. Contacts and Influence. Social Networks 1(1), 5-51 (1978).

Kleinberg, J. Navigation in a Small World. Nature, 406,845 (2000).

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