The Myth of Six Degrees of Separation

What do Santa Claus and six degrees of separation have in common? People around the world believe in them. Since we wouldn’t dare to argue about Santa Claus, we will discuss the six degrees of separation theory instead.

The six degrees of separation theory is based on research conducted by Stanley Milgram in the 1960s and 70s. Milgram wanted to learn more about the probability that two randomly selected people would know each other. In his most famous experiment, Milgram chose about 300 individuals in several U.S. cities to be the starting points and Boston, Massachusetts to be the end point of a chain of correspondence. Information packets were initially sent to "randomly" selected individuals. They included letters, which detailed the study's purpose and basic information about a target contact person in Boston. Upon receiving the invitation to participate, the recipient was asked whether he or she personally knew the contact person described in the letter. If so, the person should forward the letter directly to that person. In the more likely case that the person did not personally know the target, then the person was to send it to a friend or relative they know personally that is more likely to know the target. When the letter eventually reached the contact person in Boston, the researchers counted the number of times it had been forwarded from person to person. Among these chains, the average path length fell around 5.5. Hence, the researchers concluded that people in the United States are separated by about six people on average.

The research was groundbreaking in that it suggested that human society is a small world type network characterized by short path lengths. Milgram’s view of the problem was to imagine the population as a social network and attempt to find the average path length between any two nodes. Although Milgram himself never used the phrase "six degrees of separation", these findings are likely to have contributed to its widespread acceptance.

In the intervening decades, Milgram's findings have slipped away from their scientific moorings and sailed into the world of imagination, says Judith Kleinfeld from University of Alaska Fairbanks. According to her, Milgram's startling conclusion turned out to rest on scanty evidence and the idea of "six degrees of separation" might be the academic equivalent of an urban myth. Also Ivan Misner, author of several books about human networks, calls it a widely held belief that just isn’t true. He states that the overwhelming majority of people in Milgram's studies never got the material to the intended recipient. This is, in fact, correct because only 64 out of 296 letters in Milgram’s experiment arrived at the destination, what corresponds to about 20 %. In Milgram’s first, unpublished study, only 3 of 60 letters - 5 percent - made it. The high number of lost letters puts a big question mark at Milgram’s results. Every lost letter might indicate a longer chain, because the longer the chain, the more unlikely the final arrival of the letter (and vice versa). After all, this means, that the average degree of separation might be considerably higher than six.

When looking for more recent examples of the six degrees research, we can’t skip online communities like Facebook or Twitter. A Facebook platform application named "Six Degrees" was developed by Karl Bunyan, which calculated the degrees of separation between different people. The average separation for all 5.8 million users of the application was 5.73 degrees, whereas the maximum degree of separation was 12. In June 2009, Bunyan shut down the application, presumably due to issues with Facebook's caching policy. Users on Twitter can follow other users creating a network. According to a study of 5.2 billion such relationships by the social media monitoring firm Sysomos, the average distance on Twitter is 4.67. On average, about 50% of people on Twitter are only four steps away from each other, while nearly everyone is five steps away. Care has to be taken when, when generalizing the degree numbers of Facebook and Twitter. These networks generally consist of a specific group of mainly young people who are extremely well connected. The overall society contains many people who are not connected by electronic communities and who might even not be connected to the internet at all. Therefore, the degree of the overall society should be significantly higher than the degree of the online communities.

We can conclude that the exact degree of separation of our society remains unknown. Experiments have had weaknesses and a perfect model for our heterogeneous society has not been found and might even not exist. The degrees of online networks give us a good indication but only represent a specific part of the population. Also, we must state, that the degree of separation is probably not constant in time, which results in further questions. How much do electronic communication and online networks contribute towards a decreasing degree of separation? On the other hand, does the growing world population tend to increase the degree of separation? Maybe Santa Claus can give some answers.

Sources:

Stanley Milgram, "The Small World Problem", Psychology Today, 1967

Ithiel de Sola Pool, Manfred Kochen, "Contacts and Influence", Social Networks 1(1), 1978

Ivan Misner, “Debunking the Six Degrees of Separation”, 2007, http://www.entrepreneur.com/marketing/networking/article177986.html

Judith Kleinfeld, “Six Degrees of Separation: An Urban Myth?”, Psychology Today, 2001, http://www.judithkleinfeld.com/ar_sixdegrees.html

Sebastian Schnettler, "Mythos Kleine Welt", 2008, http://www.wiso-net.de/webcgi?START=A20&T_FORMAT=5&DOKM=1521297_ZDZI_0&TREFFER_NR=2&WID=80142-7200440-13224_10