Pattern Recognition - Violence and Mental Illness

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December 17th, 2012
09:57 am

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Violence and Mental Illness
Which of the following statements are true?

1) Most violent crime is committed by mentally healthy--i.e., not diagnosably mentally ill--people.

2) Most mentally ill people do not commit violent crimes.

3) Mentally ill people are more likely to commit violent crime than others.



All three statements are true. For example, this study states that
...a pooled proportion of 6.48% of all homicide offenders had a diagnosis of schizophrenia (95% confidence intervals [CI]=5.56%-7.54%).
Now, the population incidence of schizophrenia is about 1.1%, and the lifetime probability that a randomly chosen resident of the United States will commit at least one murder is somewhere less than 0.3%. Combined with the statistic above, we can say that:

1) About 93.5% of all murders are committed by non-schizophrenics.

2) Most people with schizophrenia do not commit murder.

3) People with schizophrenia are around five to seven times more likely to commit murder than people without.

You're welcome.

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From:mizkit
Date:December 17th, 2012 03:07 pm (UTC)
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"But we will definitely not pursue any kind of improvement in our mental health care diagnoses, treatments, and facilities in light of this funny math."
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From:st_rev
Date:December 17th, 2012 03:24 pm (UTC)
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On the other hand...

If you gave every schizophrenic individual perfect care, reducing their murder rate to the population norm, you'd only stop about 5% of all murders.

Giving every schizophrenic individual perfect care is imposssible. Schizophrenia is almost unique among mental illnessess in that it's only extremely hard to treat rather than impossible.
From:littlebbob
Date:December 17th, 2012 03:41 pm (UTC)
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Mental illness is, in general, not infectious.

This makes "overall social good" arguments in favor of improving our approach to treatment, in general, pretty bad arguments.

There are fine arguments to be made in favor of improving our treatment of the mentally ill, make no mistake. It's just that a "lowers overall cost to our society" is unlikely to be among them.
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From:st_rev
Date:December 17th, 2012 03:36 pm (UTC)
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And it gets worse. Suppose perfect care cost $5,000 per year per patient (this is absurdly optimistic). The average age of onset is about 20, so that's 50 years of care, at a cost of $250,000. To stop one murder, you'd have to give perfect lifetime care to about 100 schizophrenic individuals. That's $25 million dollars to save one life.

There are other reasons to try to help the mentally ill, but as a crime prevention measure, that is astronomically wasteful.
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From:mizkit
Date:December 17th, 2012 03:44 pm (UTC)
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*laughs* I'd never run or imagined the numbers, really. But I was more thinking of other reasons to try to help anyway, because the system is so badly damaged I'm not even sure it can be called a system.
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From:st_rev
Date:December 17th, 2012 03:54 pm (UTC)
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Letting the severely mentally ill run around free is a serious problem. The old way, locking them up, was also a serious problem. It's not clear what other options exist.
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From:mizkit
Date:December 17th, 2012 04:45 pm (UTC)
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Vastly improving lock-up is the best I can come up with, and it's not good either. I don't know.
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From:dhole
Date:December 17th, 2012 04:17 pm (UTC)
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I'm not sure that you've given sufficient evidence to support 3 -- the study shows that people with schizophrenia are more likely to kill people but murder is one of the less popular violent crimes, and there are way more types of mental illness than schizophrenia.

(If suicide counts as a violent crime, you will get a lot of depressed people committing suicide. On the other hand, I'm not sure how many agoraphobics are out there committing assault and battery.)
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From:st_rev
Date:December 17th, 2012 04:32 pm (UTC)
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I'm picking out a specific case I happen to have hard numbers for. 'Mental illness' is a clade and a bad category, but it's what people are arguing about online. A better category would be something like 'schizophrenia + bipolar disorder + antisocial personality disorder', and that category would line up with assault etc. very nicely.

Of course, 'antisocial personality disorder' is a problematic classification, as it's very close to being defined as 'the kind of crazy person who commits violent crimes'.

ETA: 'Mental illness' is NOT a clade, it's polyphyletic. I had the definition backwards.

Edited at 2012-12-17 06:41 pm (UTC)
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