Saturday, April 28, 2007

Mental Illness and Violence

I was looking for information on the extent of mental illness among prison inmates, and I found this review of the literature in the journal Psychiatric Services. It reports that "6 to 15 percent of persons in city and county jails and 10 to 15 percent of persons in state prisons have severe mental illness." This is consistent with the recent work by Bernard Harcourt that I have mentioned previously showing that there is a strong negative correlation between institutionalization rates (mental hospitals plus prisons) and homicide rates.

As the grand experiment of deinstitutionalization took place, murder rates rose. As the percentage of the population in prison rose, murder rates fell. This was even true when Professor Harcourt repeated the study using state level data. While there were a few oddball states such as Florida where the institutionalization rate seems to have no connection to murder rates, this is the exception. Almost every state had a statistically significant negative correlation, and no state had a statistically significant positive correlation.

It doesn't take a genius to see that prison is a bad substitute for mental health treatment. Some mental illnesses can be treated. Some illnesses can be brought under control (such as bipolar disorder); some can be treated at least for the symptoms (such as schizophrenia). I doubt that mental hospitals are cheaper per year per patient than prisons, but if you can treat a patient to the point where he isn't a danger to others or himself, this seems preferable to throwing a patient into a prison instead--and might, if we can figure out a way to supervise the patient's medications upon release, save some money.

Anyway, while digging around, I found a number of interesting papers about the question of violent crimes and the mentally ill. If you read most newspapers, almost any time that an article discusses mental illness, the reporter will insert a comment to the effect that the mentally ill are no more violent than anyone else. Why do they always insert this? Because this is now conventional wisdom, and like most conventional wisdom that reporters feel the need to insert in their articles, it appears to be incorrect.

This 1976 article the American Journal of Psychiatry studied patients released from Bellevue's psychiatric division in New York City, and found that they were more likely to be arrested for rape, aggravated assault, and burglary than the general population of the "catchment area" for Bellevue. They were less likely to be arrested for murder and robbery, although not much less. This study seems a bit deficient in statistical significance information. This was contrary to a number of earlier studies that found murder and robbery rates higher among released mental patients.

This 1978 study examined San Mateo County mental patients
, and found that they nine times more likely to be arrested for violent crimes than the general population of the county--and for some crimes, like murder, as much as 55 times as likely to be arrested. Now, it is possible that mentally ill people come to the attention of police, and are more likely to be arrested for that reason, but 55 times as likely? I think Harcourt's negative correlation is beginning to look correct.

There are some significant differences based on age. Not surprisingly, the mentally ill in their 50s and 60s are not terribly likely to be arrested for violent crimes--much as is true in the general population. Not all forms of mental illness seem equivalently likely to produce violent behavior. But it does appear that much of the traditional view of the mentally ill--as having a higher potential danger to public safety--has some basis in fact.

You may be wondering why that 1976 study in New York City found murder and aggravated assault rates among mentally ill comparable to the rest of the population. At the risk of being quoted out of context by a gun control advocate: there is a possibility that New York City's strict gun control laws make it sufficiently difficult for mentally ill persons released from the hospital to get hold of a gun, reducing their murder rates relative to, for example, the San Mateo County population in that 1978 paper. Aggravated assault charges usually involve a weapon--and I suppose that the inability to get hold of a gun might explain why that rate was about the same as the general population in New York City. I find this a plausible explanation because one of the arguments for why New York City had to pass its 1967 Gun Control Law was that "crazy people" (as some New York politician I saw once explain it) were buying guns and going immediately into the streets and shooting people.

Still, this suggests that gun control laws make all of New York rather like a mental hospital--one that limits access to deadly weapons. It might have more sense to have asked why mentally ill people were being released to the streets to live on steam grates.

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