A new study from the Swedish medical university Karolinska Institutet and the University of Oxford finds that the severe mental disorder schizophrenia only marginally increases the risk of committing violent crime. Rather, the overrepresentation of individuals with schizophrenia in violent crime is almost entirely attributable to concurrent substance abuse.
In the debate surrounding violent crimes referred to as "acts of madness" or the like, it is often assumed that the violence is a direct result of the perpetrator’s mental illness. Previous research suggests that people with schizophrenia, a major psychotic disorder, are at higher risk for violent behaviour. However, there has been some uncertainty as to the magnitude of this risk increase and if it can really be attributed to the violence itself or to other factors.
The new study, presented in the May 20 issue of the scientific journal JAMA, is the largest in this field to date. In it, researchers compared the rate of violent crime in over 8,000 people diagnosed with schizophrenia between 1973 and 2006, and a control group of 80,000 people from the general population of Sweden.
Twenty-eight per cent of those with schizophrenia and co-occurring substance abuse were convicted of violent crime, compared to eight per cent of those with schizophrenia and no substance abuse, and five per cent of the general population.
"Hence, the idea that people with schizophrenia are generally more violent than those without is not true," says Niklas Långström, one of the researchers behind the study. "People with schizophrenia but no co-occurring substance abuse are insignificantly more violent than people in general."
Långström hopes that the results could help alleviate fears about mental illness.
"The stigmatisation of the mentally ill increases their alienation and makes people less likely to seek the help they need from mental health services", he says. "Our results demonstrate once again the importance of preventing, discovering and treating substance misuse in efforts to reduce violent crime."
Seena Fazel, Niklas Långström, Anders Hjern, Martin Grann, Paul Lichtenstein."Schizophrenia, substance abuse, and violent crime".
JAMA. 2009 May 20;301(19):2016-23.