Teenagers who see adults fighting at home are more likely to lash out violently against others - and a quarter of them try to kill themselves each year.
Latest results from a national survey of 9700 high school students in the year 2000, released at Parliament yesterday, show that New Zealand's teenagers live in a culture where violence is common.
Half of all high school boys were hit or harmed by others at least once in the previous year, a quarter were involved in serious fights, 5 per cent had to get medical treatment after a fight and 3 per cent attacked someone else with a weapon.
Only 5 per cent came from homes where they saw adults hitting or physically hurting each other in the previous year, and only 1 per cent saw adults hitting each other more than once or twice a year. But boys from that 1 per cent of most violent homes were far more likely than other boys to be violent themselves.
Some 26 per cent of them hit others at least three times during the previous year, compared with 12 per cent of boys from other homes.
Eighteen per cent of them, compared with only 2.5 per cent of other boys, attacked someone with a weapon.
Children from the 5 per cent of homes where adults hit each other were also three times as likely as other children to be depressed, and 28 per cent tried to kill themselves.
The attempted suicide rate in the whole high school population was only about a quarter of this.
Lead researcher Peter Watson, a paediatrician at Auckland University, said the survey could not tell whether seeing violence at home actually made teenagers more violent or suicidal, or simply reflected other factors that made the whole family "dysfunctional".
"My sense, as a clinician in child and youth mental health, is that it's both," he said. "There are some young people exposed to violence in the home where that has a direct impact.
"They have post-traumatic stress disorder and anxiety problems as a direct result of witnessing violence in the home. Also, there is very strong evidence that violence is a marker of disturbed family functioning, disturbed relationships and attachment problems between kids and their parents. So it's not either/or."
The 2000 survey, funded by the Ministry of Health, was the first of its kind so there are no easy comparisons with any previous data in New Zealand or elsewhere.
The survey team has already reported on other aspects of the survey, but was asked to extract details on violence for yesterday's official announcement of a national initiative to question all women and caregivers of children arriving at public hospitals about whether there is any violence at home.
An $11 million advertising campaign to change New Zealanders' attitudes and behaviour around family violence will begin on September 4.
At the same time, the Auckland University team behind the 2000 survey is now repeating the survey in high schools to see whether anything has changed in seven years. Its results are due late next year. Dr Watson said violence had always been "part of the human condition", but the survey showed that about half of all teenagers still managed to avoid it, and that it had negative effects on the health and wellbeing of many of its victims.
Apart from depression and attempted suicide, teenagers who saw violence at home were roughly twice as likely as others to smoke, drink alcohol and take cannabis.
Girls were twice as likely as other girls to have unwanted sexual contact and boys were more than four times as likely as other boys to be sexually abusive.
The survey found that 33 per cent of both boys and girls at age 15 claimed to have had sexual intercourse, even though sex with anyone under 16 is illegal.
Twelve per cent of the girls and 3 per cent of the boys who had had sexual intercourse said they did not want to have it the first time it happened.