The way in which the individual units that constitute a network link with each other is crucial, be they sardines, neurons, people or planets. The degree of separation between nodes determines how effectively a network operates.

In networks, all nodes are connected; a node can be reached from a given start point by following those connections. Studies into network theory have focused on a particular, effective structure called the “small world” model: a good example of this is the network of neurons in your brain. Human society is structured in a similar way.

Perhaps, whilst on holiday, you’ve met someone for the first time who knows one of your friends. “It’s a small world,” you find yourself saying. Stanley Milgram put this idea to the test. Imagine you have in your possession a letter for a certain individual. You know this person’s name, occupation, and the region where they live, but you don’t know his address. Your task, in Milgram’s experiment, is to forward a letter either directly to the target recipient or someone believed to be closer to the person in question.

Milgram wanted to see how many times the letter had to be forwarded on until it reached the intended target. In this experiment every occasion the letter was sent was described as a degree of separation. If, by pure chance, you happened to know the intended person’s address and sent the letter directly to them, one degree of separation would exist. Milgram conducted several tests. In one experiment, 296 letters were sent; most went missing. 64 found their target: of those, the chain between the first person and ultimate recipient was, on average, 5.5.

From this experiment came the saying “six degrees of separation”.10

There is a slight catch with Milgram’s original experiment. If you were sent a letter out of the blue and were asked to redirect it as part of an experiment, what would you do? Chances are you would bin it. As such, Milgram’s experiment has survivor bias built into it. Chains with more than seven links are likely to have broken down. Subsequent analysis of the Milgram data has suggested that there is an average of 11 links tying people together.11

Another famous example of a small world experiment was the so-called “Six Degrees of Kevin Bacon”, which was referred to by both Mark Newman in his book Networks and Introduction and Albert-Laszio Barabasi in Linked. Author Richard Gilliam designed a game in which the players had to find how many films linked a randomly selected actor to Kevin Bacon, having appeared in the same film. For example, Elvis Presley appeared in Change of Habit, which also starred Edward Asner, who appeared in JFK as did Bacon. Elvis is separated from Bacon by two steps: in the jargon of the game, he had a Bacon number of two.

Incidentally, Kevin Bacon is not particularly “well connected”; Rod Steiger was better connected at the time Gilliam designed his game. Of importance here is the fact that all nodes (actors) in the network (Hollywood) are connected; their degree of connectedness varies and is important in its own right.

© Investment & Business News 2013

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