Police say a new assessment tool that predicts the likelihood of someone who's assaulted his or her partner doing it again, has revealed a much higher risk than expected.
A list of 13 questions used to predict whether someone is likely to reoffend in cases of intimate partner violence.
The Ontario domestic assault risk assessment was used about 3200 times from July - September.
Police say 40% of people screened in those cases fell in the highest risk category - suggesting further offending is likely to happen sooner, more frequently and be more severe.
That compares to a study in Canada that found only 7% of men screened there fell into that category.
Inspector Briggitte Nimmo says the results are now being audited because the police want to use them in courts from next year to oppose bail, at sentencing and at parole hearings.
Detective Inspector George Faalogo says the results raise hard questions about the nature of violence in New Zealand.
"It gives us clear direction as to where we should be allocating our resources to prevent violence happening and also of course gives us the ability to predict when violence happens again."
Hesays the results are now being audited by an independent researcher.
Waitakere anti-violence services manager Poto Williams say it is important the police don't just put everything into combating people at the high risk end of reoffending.
"There are a whole group of people who sit under that catchment for whom family violence is a really destructive and horrible experience that we're not supporting very well, and eventually they'll become critical as well," she says.