It’s often remarked that stockmarket manias and panics are contagious, as though there’s some virus spreading through the markets, infecting the participants and causing their irrational behaviour. Of course, this is usually meant as a metaphor rather than something to be taken literally – it’s a nice conceit that there’s a disease “out there” causing us to all do stupid things all together.
However, humans are social animals, we live in social networks and networks are prone to attack at their weakest points. Models of how real and virtual diseases spread – the study of epidemiology – can give us clues as to what’s really happening when everything goes screwy. And it turns out that the more connected we are the more danger we’re in.
Rod Steiger’s Network
Most people are aware of the Kevin Bacon game which measures actors by how close they’ve come to acting with the prolific star of Flashdance. Someone who’s acted in the same film with Kevin has a Bacon number of 1, someone who’s acted with someone who’s acted in the same film as him has a number of 2, and so on. By tracing out this network researchers have been able to piece together the network of social connectedness amongst Hollywood actors. In fact it turns out that Mr Bacon isn’t anywhere near the most connected actor, and the thesps should actually be linked by the Rod Steiger number.
What’s really interesting, however, is what happened when the researchers looked at how the actors were connected. It turned out that the average actor has an average number of connections but that a few, key, thespians held the network together. These critical “nodes” had far, far more connections than most of their fellow luvvies. If you think of this as a network, then if you could somehow remove the key players then suddenly the whole thing would fall apart.
Scale Free Networks
It turns out that this is a decent model for the way most social networks link and, in particular, for the way diseases spread. Epidemiologists have a real interest in understanding this because they’re interested in figuring out how to prevent the spread of diseases like
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Philip R. Davis is a founder Phil's Stock World, a stock and options trading site that teaches the art of options trading to newcomers and devises advanced strategies for expert traders...
Ilene is editor and affiliate program
coordinator for PSW.
