The process for catching these people is equally elegant

Saturday, January 6th, 2018

Scott Alexander shares some highlights from his notes from a forensic psychiatry conference:

Contrary to popular belief, the insanity defense is not overused. It’s used in only about 1% of felony trials and successful only about a quarter of the time it is used. 90% of people who successfully plead insanity had been diagnosed with a disorder before they committed their crime.

Felons found insane usually get locked up in forensic hospitals even longer than sane felons are locked up in prisons. Some statistics say that by pleading insanity you increase your time behind bars by 50–100%

For some reason, there is a law saying juries are not allowed to be told what will happen to defendants if they return a certain verdict. Juries assume that if a defendant is found “not guilty by reason of insanity”, they will be released scot-free. Although this is completely false, no one is allowed to tell the jury this. So it’s really hard to win an insanity defense simply because juries think it will mean a felon will be put right back on the streets.

Forensic psychiatrists have become very effective at determining which criminals who plead insanity are “faking it”. They usually rely on patterns of mental disease which psychiatrists know but criminals don’t. For example, they’ll start by asking “Do you hear voices?”, and most fakers, anxious to please, say they do. Then the psychiatrist will ask questions like “Which side of your head do the voices come from?” and “Do you ever have smells associated with the voices?” Still eager to please, the fakers will choose a side of the head for their voices to be on, and make up smells that happen at the same time as their voices. But real schizophrenics don’t generally hear their voices to one side or hallucinate smells, so this decreases the likelihood that they’re telling the truth. Some of these questions are very tricky – for example, one psychiatrist asks both “Do you ever hear secret messages for you from the TV or radio?” and “Do cats and dogs ever give you secret messages?”. The first is very common in mental illness; the second practically never happens. Unless you’re a psychiatrist yourself, you’re not going to know these things and you’ll end up claiming symptoms that make no sense.

Some criminals also claim to be mentally retarded, especially in states where it’s illegal to execute retarded people. The process for catching these people is equally elegant. They are asked to take a multiple-choice vocabulary test with easy, medium, and difficult words. Real mentally retarded people will do okay on the easy words but perform at chance on the medium and difficult words. Fakers will also do okay on the easy words – they are smart enough to understand that even mentally retarded people know some things – but then they intentionally throw the medium words and do worse than chance. On the difficult words, the fakers honestly don’t know them and so they go back to performing at chance again. Computers can detect these patterns and easily and confidently point out a fake.

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