Gun killings in New Zealand have declined the most in an international comparison - even though this country has less strict licensing laws than Canada and Australia.

A forthcoming article in the peer-reviewed Journal of Interpersonal Violence, published by United States-based Sage Publications, found New Zealand had "the most pronounced decline in firearm homicide over the past two decades".

The study suggests unemployment rates and the availability of heroin are more significant factors in firearm homicides than gun control.

In recent weeks, New Zealand has heard calls to make changes around gun laws after two police officers and their dog were shot in Christchurch and a Feilding farmer was murdered in his driveway with a shotgun.

Last year, Jan Molenaar killed a police officer in Napier with his arsenal of unregistered firearms, prompting many to question whether police should keep closer tabs on guns.

Police Association president Greg O'Connor, who advocates arming police officers, said the decline in firearm homicides showed New Zealand had well-balanced gun licensing.

"Particularly in New Zealand, you can go hunting and do your bit for ecology, because you're mostly hunting pests anyway," Mr O'Connor said.

"I would be very disappointed if as a result of the actions of criminals in New Zealand, there was an encroachment against lawful gun-owning people."

But even as general firearm homicides declined, more police were getting shot and officers needed protection. Organised crime and P were likely to be driving up attacks against police, Mr O'Connor said.

The study's lead author, Samara McPhedran, said from an international point of view, New Zealand's gun laws "have been just about right".

A former director of the United Nations Centre for Peace and Disarmament in Asia and the Pacific, Tsutomu Ishiguri, has voiced similar sentiments, describing New Zealand gun control as "world class".

A toughening of Australian gun laws in 1996 had no effect on the downward trajectory of gun homicides, Dr McPhedran said.

The study observed trends for the three countries between 1986 and 2007.

A statistical comparison between the countries found per capita rates in Canada and Australia had tracked similar lines.

But New Zealand's rate had fallen further every year, on average, than either country. This was despite New Zealand being the only country that did not require registration of all firearms.

The study also found that typically between 80 and 90 per cent of homicides were committed using illicitly owned firearms - although it was extremely rare for a stolen firearm to be used.

The findings "indicate dissociation between firearm violence and legislative approaches to firearms ownership", the study says.

"Legislative reform does not influence the population of individuals who commit firearm violence."

Licence required
* NZ: Yes
* Canada: Yes
* Australia: Yes

Pump-action shotguns banned?
* NZ: No
* Canada: No
* Australia: Yes

Registration required for all firearms?
* NZ: No
* Canada: Yes
* Australia: Yes

Longarm licence length (years)
* NZ: 10
* Canada: 5
* Australia: 5

Change in gun homicide rate (average per year)
* NZ: -7.7%
* Canada: -1.7%
* Australia: -6.6%