Also from the New York Times is Revising the Script on Mental Illness and Violence which attempts to explain why we think of the mentally ill as violent when the vast majority are not. There's some interesting facts in this article, taken from a study by the Duke University Medical Center.
- The incidence of violence is 5 times as high among people with serious mental disorders (e.g., schizophrenia, major depression, and bipolar disorder) as it is among those with no psychiatric illness.
- People who use alcohol or other drugs are 12 to 16 times more likely to be violent as non-users.
- Psychiatric patients have much higher rates of alcohol and substance abuse than the population as a whole.
- When alcohol is controlled for, violence among subjects drops to 7 percent from 20 percent.
The conclusion being drawn from all this is that violence is related to the level of psychiatric symptoms. Decent conclusion. So is the conclusion that alcohol has a lot to do with it.
But his conclusion as to why people believe that mentally ill people are more violent? It's the media. He throws out the Jeffrey Dahmer case as an example of the media causing us all to to believe this. But he's wrong really.
It's really something called availability error.
John Allen Paulos writes about it frequently. Anxiety, fear, and the force of a vivid anecdote can, for example, mask the mathematical distinction between the rate of incidence of some condition and the absolute number of instances.
In other words, the absolute number is more important than the rate in our minds. Most urban dwellers have encountered the mentally ill. And most have an experience or two with them becoming threatening or violent. They may not see it often. They may only see it a couple of times in a lifetime, but that is much more important than the statistic. Because it is personal, for one. It has more impact on our consciousness. And because it is negative and extraordinary. We do not remember things that do not stick out. Occurrences that are unusual, different from our daily routines, these we remember. It trumps the statistics we read in the newspaper and also outweighs all the non-violent mentally ill people we run into every day. Those are not as available to us as the bad experience.
How many people have had a mentally ill person do something unusual in a nice way, that didn't also scare us in other ways? I'm sure it happens. But it happens quite a bit less.
Thus, our perception.