The odds of a 22-year absence of mass shootings in Australia since 1996 gun reforms being due to chance are one in 200,000, new research reveals.

Published today in the Annals of Internal Medicine, scholars at the University of Sydney and Macquarie University used mathematical techniques to test the null hypothesis that the rate of mass shootings in Australia before and after the 1996 law reforms is unchanged.

The National Firearms Agreement, enacted after the Port Arthur massacre in Tasmania in which 35 died and another 23 were seriously injured, saw the destruction of more than a million firearms -- perhaps a third of the country's private gun stock.

The Agreement included uniform gun registration, repudiation of self-defense as a legitimate reason to hold a firearm license, mandatory locked storage, a ban on mail order sales and standardized penalties, and the banning of semi-automatic rifles and pump action shot guns from civilian ownership.

Its provisions were subsequently enacted in national, state and territory legislation across Australia.

In the 18 years up to and including the Port Arthur massacre in 1996, there were 13-gun homicides in which five or more people died, not including the perpetrator. In the 22 years since, there have been no such incidents.

"Most people hear these starkly contrasting numbers and conclude that Australia's gun law reforms effectively stopped firearm massacres here," says the paper's lead author, Emeritus Professor Simon Chapman of the University of Sydney.

"However, some scholars and members of the gun lobby have argued that since mass shootings are relatively rare events, the concentration of incidents in one decade and their absence in another decade is merely a statistical anomaly."

For example, Australian researcher Dr Samara McPhedran writing in The Conversation said: "Mass shootings are rare events, and the long gap between incidents post-1996 may simply reflect a return to a more 'normal' state of affairs, similar to the years before 1987."

"This was no accident," says the new study's co-author Associate Professor Philip Alpers, from the University of Sydney. "Australia followed standard public health procedures to reduce the risk of multiple shooting events, and we can see the evidence. It worked.

"Gun lobby-affiliated and other researchers have been saying for years that mass shootings are such rare events it could have been a matter of luck they dropped off in the wake of Australia's gun control laws," says Alpers. "Instead, we found the odds against this hypothesis are 200,000 to one."

In related news, Tasmania's re-elected Premier has defended the Liberals' policy to relax the state's gun laws, despite an outcry from survivors of the Port Arthur shooting.