Despite claims by the gun lobby, most violent individuals don't have a mental illness, write the authors of a "For debate" article published online by the Medical Journal of Australia.

Dr Michael Dudley and colleagues from the University of New South Wales, the University of Wollongong and the University of Sydney, wrote that it is timely to examine how national firearms regulation has prevented injury in the 20 years since the Port Arthur massacre.

Studies have confirmed that people with mental illness are more likely to be victims of violent crime. For example, almost half of those who die at the hands of US police have some kind of disability.

The authors argued that most mass murderers don't have an identifiable, severe mental illness and instead often have maladaptive personality configurations.

"Although mass murderers who seize media attention often seem to suffer from psychosis, no research clearly verifies that most are psychotic or even suffering from severe mental illness," the authors wrote.

In the case of Martin Bryant, the lone gunman who used semi-automatic weapons to kill 35 people at Port Arthur, four forensic psychiatric reports found he was suffering from a "personality disorder with limited intellectual and empathic capacities". The sentencing judge concluded that he was "not suffering from a mental illness."

Recent gun massacres in the US have seen calls for better screening of mentally ill populations for violence risk, however the authors believed this was misguided.

Because people with mental illness are not categorically dangerous, and because of sensitivity and specificity problems with screening for violence, "psychiatrists are no better than laypeople or chance at prediction".

They wrote that clinicians have a role in monitoring and assisting regulation of firearm access, particularly in high-risk populations such as children, adolescents, suicidal people, domestic violence victims and perpetrators, farmers and rural residents, and police and security employees.

The authors argued that wider gun control measures should be the more pressing debate.

"The campaign to deflect social concern over firearms availability into a debate about whether people with mental illness histories should access such weapons should be exposed as a calculated appeal to prejudice," they concluded.

Article: The Port Arthur massacre and the National Firearms Agreement: 20 years on, what are the lessons? Michael J Dudley, Alan Rosen, Philip A Alpers and Rebecca Peters, Medical Journal of Australia, doi: 10.5694/mja16.00293, published online 23 May 2016.