Following the crowd—how far does this idea go?

In our class textbook, Professor Kleinberg and Professor Easley write that “an information cascade has the potential to occur when people make decisions sequentially, with later people watching the actions of earlier people, and from these actions inferring something about what the earlier people know … In such a situation, a cascade develops when people abandon their own information in favor of inferences based on other people’s actions” (306).

Does then, a chain of suicides qualify as a result of an information cascade? Can there be a cascade of suicides? In his book, “The Enigma of Suicide,” George Howe Colt reveals a great deal of insight on the causes and triggers of suicide. There have been many studies that show suicide rates suddenly increase after a suicide is romanticized—either through a common television show or a public suicide of a celebrity. David Phillips, a sociologist from Princeton University, did some research on this idea:

Checking the vital statistics of the United States against The New York Times index for front-page stories on suicide since World War II, he found that suicides increased significantly in the month after a highly publicized suicide story. The greater the publicity, the greater the increase. For instance, the suicide of Marilyn Monroe in 1962 spurred a 12 perfect jump (197 more suicides than would have been expected in the month following her death) (91).

This is both a very interesting and depressing idea to consider. If people see other people committing suicides, do they obtain information that is more powerful than their own private information? Phillips coined the term “Werther effect” to describe this ‘copycat suicide’ phenomenon.

But what possible information could individuals receive from reading about a suicide that would encourage them to also kill themselves? Phillips discuses that there are already many depressed people in the world who may not realize they’re unhappy. And when they see a story such as Marilyn Monroe’s suicide, they “become aware that they are unhappy and maybe also become aware of an option to end their happiness” (91).

Let us now consider whether suicides actually have the ingredients of a typical information cascade model.

1)  Is there a decision to be made? Yes —put a bit cynically: “To be or not to be: that is the question.”

2)  Do people make the decision sequentially, where each person can observe the choices made by those who acted earlier? Certainly. An initial suicide (such as Marilyn Monroe’s) may encourage a large group of individuals to commit suicide. These suicides will then be publicized in the news, and may lead to further suicide from people who read about it.

3)  Does each person have some private information that helps guide his information? Yes. Each person knows about his own life. Each person (in the model) has his own personal reasons for being depressed.

4)  Is it the case that a person cannot directly observe the private information that other people know, but he or she can make inferences about it from what they do?  This is exactly the case. Nobody knows for sure why someone else kills himself. But given the situation, one can probably infer some sort of depression.

Note that the properties described in numbers 1 to 4 have been taken from our Econ 2040 Networks textbook by Professors Kleinberg and Easley (307).

How far can this analysis actually be taken? Let’s see if we can apply Bayes’ Rule to calculate when a person would actually commit suicide. Disclaimer: I personally do not believe that suicide should ever be an option. However, purely as an academic exercise, it is interesting to derive when it seems “rational” to commit suicide (from the person committing suicide’s perspective).

We have to find the probability that one should kill himself given what he has seen and heard regarding recent suicides. If this probability is greater than a half, then from a mathematical standpoint, it would seem rational to kill oneself. Calculating this probability is a lot more involved than just plugging in numbers into a formula. For instance, what are the prior probabilities that one should kill himself or one should continue living? These depend entirely on an individual’s lifestyle and situation before reading about other people’s suicides.  Similarly, what is the probability of what one has seen and heard given that one should kill himself? This is delving into deeper issues about society. If one individual should kill himself, what does that imply about the state of the rest of society?

Clearly, finding values for these probabilities is a very complex process. In fact, one could argue that it is impossible to quantify any of these probabilities. Though the decision to kill oneself is certainly dependent on all of the factors listed earlier, the probabilities are determined by an individual through his intuition, survival instinct and experiences in society rather than through a mathematical process. The only person who can know for sure whether a suicide will occur is the person who is about to kill himself.

If you want to read more about Phillip’s experiments, read chapter four, “Something in the Air,” from George Howe Colt’s “The Enigma of Suicide.”