TEN years of suicide data after John Howard's decision to ban and then buy back 600,000 semi-automatic rifles and shotguns has had a stunning effect.

The buyback cut firearm suicides by 74 per cent, saving 200 lives a year, according to research to be published in The American Law and Economics Review.

A former Australian Treasury economist, Christine Neill, now with Wilfrid Laurier University in Ontario, Canada, said she found the research result so surprising she tried to redo her calculations on the off chance the total could have been smaller.

''I fully expected to find no effect at all,'' she told the Herald. ''That we found such a big effect and that it meshed with a range of other data was just shocking, completely unexpected.''

Mr Howard's agreement with the states to ban and buy back more than 600,000 weapons after the massacre at Port Arthur in April 1996 cut the country's stock of firearms by 20 per cent and roughly halved the number of households with access to guns.