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Information Cascades and Mob Mentality

If you grew up in an American public school system there is a good chance you had to read Lord of the Flies at some point.  As you read the tale of school boys stranded on an island at some point your teacher throws out two words: “Mob Mentality.”  Even if you haven’t read William Golding’s acclaimed book, you might know what mob mentality is, and you’ve almost definitely experienced it to some degree.  But just if you are unfamiliar here is a definition:

Herd mentality, or mob mentality, describes how people are influenced by their peers to adopt certain behaviors, follow trends, and/or purchase items. Examples of the herd mentality include stock market trends, superstition, home décor, etc.

Mob mentality is describing and information cascade.  Take this website that gives ten rather famous examples of mob mentality, although it might not always be considered a mob:

Let’s look a little deeper at one of the examples, say number four, the Salem Witch Trials.  Here is a quote from the article describing the event: “Salem officials started arresting suspected witches based on the flimsiest evidence (accusations from little girls), and the town went along with the whole thing, relishing in the witches’ destruction.”

Here we go from flimsy evidence to the town going along with the whole thing.  And in this we see the peculiar quality of information cascades, in that often they are really misinformation cascades.  All an information cascade requires is a few people to be convinced by the evidence of some fact, in this case townspeople are conducting witchcraft, and then all of a sudden you have a whole lot more people coming along for the ride.

But what is really required for an information cascade to lead to something like false accusation of witchery leading to public hangings?  This sociological question is probably a good deal messier than the market interactions that information cascades are so often used to describe; however, the principle should remain the same.  If you can convince a few people that something is true, then it becomes much easier to convince many.

Yet this also begs the question that if there are plenty of people who are convinced of something why aren’t there always information cascades; why don’t all cults grow exponentially after hitting a certain threshold? In these mob mentality examples we see that there is also required validity to the initial proponents of an idea. In the Salem witch trials the town doctor was convinced that some girls were possessed and that there was therefore witchcraft at work.

Information cascades, aren’t just about numbers of proponents, and amount of information but also the reputation, or validity, of proponents. So perhaps we can rest a little easier knowing that crazy people who think people of your race, religion, country, etc. should [insert unpleasant verb here], often don’t have the validity even if they do have the numbers to instigate a movement, and there is not information to the contrary. So sleep easy, knowing that the chances of a mob beating down your door tonight are really, really low.



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November 2014