The study – noteable for having by far the largest sample for a study of its kind – challenges previous research claiming a person with schizophrenia can be between four and ten times more likely to commit violence.

The JAMA journal study found substance abuse co-morbidity was a significant key predictor of violence, and not schizophrenia.

The research reported that while 28 per cent of people with both schizophrenia and substance abuse were convicted of violent crime, only eight per cent of those with schizophrenia and no substance abuse were convicted. This compares with a five per cent rate of convicted violence of the general population.

The study, published this month, examined violent crime in 8,003 people diagnosed with schizophrenia between 1973 and 2006 with a control of 80,000 people from Sweden.

The study concluded that “the association between schizophrenia and violent crime is minimal unless the patients is also diagnosed as having substance abuse comorbidity.”

One of the study researchers, Dr Niklas Långström, associate professor at the Centre for Violence Prevention at the Karolinska Institute in Stockholm, Sweden said the idea that people with schizophrenia are more violent is "not true."

"The public perception of the dangerousness of psychiatric patients is pervasive and is a key factor in their stigmatization, partly influenced by selective media coverage of high-profile cases," the researchers wrote.

The study's sample number was more than the combined samples of all previous similar research.

Earlier this month The Zito Trust, which for 17 years called for more controls over violent psychiatric patients closed, declaring its objectives had been met, particularly through a new mental health act which came into effect last year.

Reference: Seena Fazel; Niklas Långström; Anders Hjern; et al. Schizophrenia, Substance Abuse, and Violent Crime
JAMA. 2009;301(19):2016-2023 (doi:10.1001/jama.2009.675)