The proportion of crimes attributable to mental disorders in the population (population attributable risk, PAR) is estimated to be 5.2% for violent crimes and 15.7% for arson 1. However, only a minority of crimes committed by mentally ill defendants is directly attributable to the underlying mental disorder 2. The relationship between crime and mental disorders is confounded by socioeconomic status, previous institutionalization, coexisting substance abuse, and personality disorders 3. We had the unique opportunity to examine the PAR for crime fully attributable to mental illness, as accountability for indicted crimes is routinely assessed in pre-trial reported defendants in the Netherlands 4. A severe psychiatric disorder, usually of psychotic nature, is a necessary condition for a finding of “not accountable” and absolves a person of guilt. The total number of crimes and defendants between 2000 and 2006 was obtained from the national Dutch registry. The PAR of crimes fully attributable to mental disorders was calculated as the fraction of persons deemed “not accountable” out of the total number of defendants.
From the 21,130 pre-trial psychiatric reports in the Netherlands made between January 1, 2000 and December 31, 2006 (1.5% of the total of 1,403,107 defendants), 1,002 defendants were considered unaccountable, amounting to a PAR for all crimes of 0.07%. The PARs for arson (0.57%), rape and other sex-related crimes (0.24%) and violent crimes (0.16%) were higher, whereas the PARs for burglary/theft (0.02%), drug-related crimes (0.002%) and fraud/deception (0.001%) were lower. Of the “not accountable” defendants, 894 persons (89.2%) had a psychotic disorder, 51 persons (5.1%) had an affective disorder, 38 persons (3.8%) had a psycho-organic syndrome and 27 persons (2.7%) had an IQ lower than 71. Comparable to other studies, the overall prevalence of psychotic disorders was 12.5% 2,5.
In conclusion, we found that the PAR of crimes directly attributable to mental disorders is very small (0.07%), although not absent. Our findings are at odds with earlier described PARs of 5.2% for violent crimes and 15.7% for arson 1, as we examined only crimes fully and directly attributable to mental illness. As there are multiple confounders of the relationship between crime and mental disorders 2,3, we think this is a more accurate reflection of the proportion of crimes attributable to mental disorders.
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