There's been a 22-year-long absence of mass shootings in Australia since 1996 gun reforms were put in place. Now a study has shown that the odds this absence is purely due to chance are one in 200,000.

Some, including members of the gun lobby, have argued that since mass shootings are rare events, the concentration of incidents in one decade and their absence in another 10-year period is only a statistical anomaly.

Researchers at the University of Sydney and Macquarie University used mathematical modelling to test the theory that the rate of mass shootings in Australia before and after the 1996 law reforms is unchanged.

Australia, which has not had a mass shooting since 1996, is often used in the US as an example of a country where tough gun laws have had an impact.

Over the same period, the United States has suffered more than 90 mass shootings.

Australia's National Firearms Agreement, brought in 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, about one third of the country's private gun stock.

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

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 Simon Chapman of the University of Sydney, lead of the study published today in the journal Annals of Internal Medicine.

Some disagree. Australian researcher Dr Samara McPhedran 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."

However, the latest study's co-author, Philip Alpers, from the University of Sydney, says Australia followed standard public health procedures to reduce the risk of multiple shooting events and it has 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."

This article was originally published by Business Insider.

More from Business Insider: