As if on cue, a major study about the relationship (if any) between mental disorder and crime has appeared just when everyone's talking about that.
Although having said that, people seem to be interested in that issue most of the time nowadays, in the UK at any rate, with schizophrenia topping the list of supposedly scary syndromes.
So - should we be worried?
The new research, from Australian team Morgan et al, surveyed everyone born in the state of Western Australia between 1955 and 1969. About 1.6 million people lived there over the course of the study so this was a big project.
By linking local records of arrests over the period 1985 to 1996 to the database of psychiatric diagnosis, the researchers were able to examine disorder-crime correlations in the entire population - meaning that there was no possibility of bias.
So what happened? Here's some highlights:
32% of psychiatric patients had been arrested at least once. Unfortunately, it's not clear what the rate was in the general population, but that falls into the range of overall arrest rates in most countries.
11% of those arrested had a psychiatric diagnosis. This rose to 20% of arrests for violent offences.
0.8% of suspects had schizophrenia, rising to 1.7% for violent offences.
The number of arrests in people without a disorder fell over the period 1985-1996, reflecting the well-known fact that people commit fewer crimes as they get older. However, in psychiatric patients, there was no change over time.
For murder, 30% of suspects had a psychiatric history while 3% had a diagnosis of schizophrenia.
Both substance abuse and personality disorders were associated with higher arrest rates than schizophrenia, but schizophrenia in turn was higher than depression, anxiety, and other miscellaneous disorders.
Although only 1.7% of violent offenders had schizophrenia, those with the disorder were somewhat more likely to involve strangers, and to take place in public places, and less likely to target family and partners.
Overall this confirms that the great majority of crimes, including violent ones, are not committed by people with mental illness, and that your chance of getting 'murdered by a lunatic' is incredibly low. This strikes me as the only statistic that matters to most people.
There's a long-standing debate over whether people with various disorders are more likely to commit crimes than they would be if they didn't have one, the relative risk. While interesting, this is a purely academic question. What the rest of us need to know is the absolute risk, and this is low.
Morgan VA, Morgan F, Valuri G, Ferrante A, Castle D, and Jablensky A (2012). A whole-of-population study of the prevalence and patterns of criminal offending in people with schizophrenia and other mental illness. Psychological medicine, 1-12 PMID: 23234722
