The number of babies dying from deliberately inflicted head injuries increased almost four-fold since 1991, with damage seen akin to that suffered in car accidents, a new study says.



In the first study of its kind in New Zealand, researchers examined data from Auckland's Starship Hospital and the Auckland city forensic pathology department, examined clinical records, autopsies, and police reports from 1991 to 2010.



It arose from a need to give courts and clinicians a large base of local data as a reference point.



From the data, all fatal head injuries over the period were classed as inflicted or accidental, based on confirmed history or confession.



When a person's history was not available, Starship's conclusion from the multidisciplinary child protection team was used.



Of the 167 cases identified in the study period, 126 injuries were classified as accidental, and 37 as inflicted. Four were not able to be classified.



Overall, the rate of babies dying from head injuries remained stable, but the rate of inflicted fatal head injuries nearly quadrupled, and the rate of accidental fatal head injuries halved.



The study found a higher incidence of both accidental and inflicted injury was seen in Maori children compared with European children.



Dr Simon John, the lead researcher of the study, designed the study so New Zealand courts and clinicians could refer to local data.



"People were giving evidence in child abuse cases, and we had no local data," John said.



"With child abuse, there is very rarely a confession, especially with young babies – it all becomes speculation."



Although the data is from Auckland, because Starship has the country's only dedicated paediatric intensive care and paediatric neurosurgical services, it could be considered reflective of the national picture, he said.



Starship is also the national tertiary referral centre.



"If you have a serious head injury, you're going to end up in Auckland," John said.



"This is real, it's not an impression."



One of the key findings was head injuries from fatal car accidents caused changes also seen in children whose fatal injury was inflicted.



Children's Commissioner Dr Russell Wills, who was the paediatrician for Plunket and a community paediatrician at Hawke's Bay Hospital, said this showed what New Zealand paediatricians had claimed for years - that babies could not die from head injuries equivalent to "a little pat or shake."



"One of the arguments from the defence is that trivial trauma can cause these findings," he said.



"If you find these findings . . . it's not from a trivial shake, it's very high energy, like you'd have in a motor vehicle accident."



Because of New Zealand's reliance on international research in court, overseas "hired gun" experts were able to come here and say there were potentially innocent explanations, or mild trauma could have caused the findings, he said.



"Local data and patterns are important to know, and give us confidence in our recommendations to court," Wills said.



Wills said over the 20 years studied, several factors could have led to the dramatic increase in inflicted injuries, including a sharp increase in teenage pregnancies, sole parenthood, and most likely an increase in domestic violence.