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The study, published in the New Zealand Medical Journal today, found that between 2000 and 2009 there were 8006 serious non-fatal assaults, with 76% of all victims men (6335). From 2003 to 2008, the rate of serious assaults a year increased by 50%.
The study's lead author, Emeritus Prof John Langley, of the university's Injury Prevention Research Unit, said it threw into serious doubt claims based on police and judicial statistics that New Zealand was becoming a less violent society.
"Police statistics are just not a reliable source for reporting trends, because they are influenced by changes in reporting behaviour and changes in recording behaviour," Prof Langley told the Otago Daily Times.
For example, after a domestic violence campaign, the number of cases reported to police could go up, while the number of actual instances remained the same.
The statistics used in the study were reliable as they were based on hospital admissions in cases where people had a 6% or greater chance of dying.
The study showed that among women, the serious assault level had fluctuated over the nine-year period, but for men, particularly in the 15-24 age-group, the numbers had risen - particularly between 2004 and 2009.
The most common method of injury was bodily force, followed by use of a blunt object, then use of a sharp object or knife. Head injuries accounted for 72.6% of all serious non-fatal injuries.
The most common location of serious assaults for men - where the location of the incident was known - was on streets and highways (1397), while the most common location for women was in the home (855).
Maori accounted for 48% of women victims in serious non-fatal assaults and 32% of male victims.
In total, the serious assaults from 2000 to 2009 required 35,186 hospital bed days.
Writing in the Medical Journal, Prof Langley said the trend was concerning, "especially since there is no evidence of any recent abatement".
A large proportion of serious assaults involved young to middle-aged men assaulting men in the same age bracket.
Despite this, historically, the prevention focus had been on domestic violence.
"While this mismatch between the burden and prevention is starting to be addressed, I question the adequacy of our prevention responses," he said.
One way to address the problem was to target excessive alcohol consumption, which was a common factor in many assaults.
It was concerning the Government had indicated it did not intend to restrict alcohol advertising, or introduce higher taxes on alcohol, which could have a "significant and relatively rapid" effect on the number of assaults.