Family violence costs New Zealand more than its annual export earnings from the forestry sector, a new study has found.
The first comprehensive update of the cost of family violence since 1994, prepared by economist Suzanne Snively for Sir Owen Glenn's inquiry into family violence, puts the cost at between $4.1 billion and $7 billion a year - up from just $1 billion in 1994.
The high-end figure works out at just over $1500 a year for every person in New Zealand - more than double an estimate for Australia, using the same methodology, of NZ$675 per person.
Even the low-end cost is higher than the $3.9 billion that New Zealand earned from forestry exports last year.
However, the wide range of cost estimates reflects extreme uncertainty about most of the parameters used to calculate the final costs.
Estimates for the prevalence of child abuse range from 1.9 per cent a year to 28.2 per cent, while the estimated prevalence of intimate partner violence against women ranges from 2.7 per cent to 23.6 per cent.
The authors tested their estimates, based on Australian methodology, with workshops for experts in Auckland and Wellington who concluded that the true prevalence rates may be even higher.
"It cannot be overstated that the advice received from professionals working in these areas is that even these 'high-end' prevalence rates seem likely to be conservative estimates," the report says.
The low-end estimates were based on the Ministry of Justice's 2009 Crime and Safety Survey, which found that 2.7 per cent of women and 1.7 per cent of men said they had suffered intimate partner violence in the previous year.
The low-end child abuse rate of 1.9 per cent was based on cases of child abuse and neglect that were substantiated by Child, Youth and Family Services (CYFS).
A "moderate" estimate was developed based on a 2003 Auckland University survey of women in Auckland and North Waikato which found that 18.2 per cent of women had experienced intimate partner violence in the past year. Violence included physical, sexual and psychological abuse.
This estimate used a Canadian study finding that 1.9 per cent of men experienced such violence in the past year. For child abuse, it used a prevalence rate of 9.4 per cent based on all cases notified to CYFS whether they were found to be substantiated or not - this was because many of the cases were notified by police because children were present during intimate partner violence, which is considered to affect children adversely even if actual "child abuse" was not substantiated.
The high-end scenario used a finding that 23.6 per cent of women born in Christchurch in 1977 had experienced intimate partner violence in the past year when they were interviewed at age 25 in 2002. That study controversially found no statistical difference between victimisation rates of women and men, so on that basis the high-end scenario assumes that 18.2 per cent of men suffered intimate partner violence in the past year, based on the 2003 Auckland University survey.
The high-end estimate of child abuse is based on a 2012 report by West Auckland's Wave Trust which said police reported only a third of family violence incidents where children were present to CYFS. The moderate child abuse estimate of 9.4 per cent was therefore trebled to 28.2 per cent.
Costs were then estimated in six categories: pain, suffering and premature death (51 per cent of the total costs), reduced productivity (14 per cent), administrative costs of justice and social services (12 per cent), increased consumption costs due to separated partners living in separate households (10 per cent), welfare costs (8 per cent) and health costs (5 per cent).
Victims of intimate partner violence accounted for 65 per cent of the total costs, children 16 per cent, employers (through reduced productivity) 13.6 per cent and perpetrators 5.5 per cent.
The Glenn inquiry plans to use the analysis to estimate the cost savings of policies to tackle family violence. Its final "blueprint" report is due before Christmas.