Up to 253,000 people are estimated to have been abused in care in New Zealand between 1950 and 2019, with the number of people passing through care judged to be six times higher than previously thought.

The Royal Commission of Inquiry into Abuse in State and Faith-based Care has released two research reports by consultancy agency Martin Jenkins and an internal report by the inquiry's research team.

It was previously thought more than 100,000 passed through care 1950 to 1999, but the research showed an estimated 655,000 people passed through care between 1950 and 2019. It puts between 17 and 39 per cent of those in care to have experienced abuse. "Even on the most conservative indicative estimates, there has been more abuse in care than previously thought."

Chair of the royal commission, Judge Coral Shaw, said the figures were deplorable, including there being more people passing through state and faith-based care than previously known. "This study has also identified key gaps in New Zealand-specific abuse prevalence data, particularly for certain population groups such as Māori, Pacific and disabled people."

Keith Wiffin, who was abused in the 1970s at Epuni Boys' Home, said it was "a truly mindboggling figure, especially when you consider for much of that period the country's population wasn't much more than three million".

"I'm shocked by it and I think the nation will be as well."

Going by the research estimations, only a minute amount of witnesses and survivors of abuse in care had registered with the inquiry. As of late August, 1756 survivors and witnesses had registered with the Inquiry. Of those, nearly half of the survivors reported abuse in state care, and 11 per cent reported abuse in faith-based settings.

Wiffin was overwhelmed to see such staggering figures – including the average lifetime cost for an individual abused in care.

Victim Keith Wiffin said it was "a truly mindboggling figure".

Research puts the average lifetime cost in 2019 to be approximately $857,000. On the estimation there were between 1250 and 2740 people abused in care last year, the lifetime cost for them alone reaches $2.35 billion. Broken down, about $184,000 was costs to the economy for increased spending on things like healthcare and state costs and the remaining $673,000 was a non-financial cost reflecting pain and suffering - and premature death.

"Applying the same average lifetime cost per survivor suggests total costs between 1950 and 2019 of between $96 billion and $217 billion," the research said.

Wiffin said that shows a "monumental impact" on not only the abuse survivors but also the country as a whole.

"You cannot have that scale of a tragedy and that scale of abuse without there being very serious systemic flaws and failures that have led to it."

The over-representation of Māori in the figures was "heart-breaking" in Wiffin's eyes. The research stated "clear evidence" of Māori over-representation from "at least the 1960s, if not earlier". It was a figure that had remained high: "By 2018 the proportion of Māori was 69 per cent for all 'out of home' placements and 78 per cent for all youth justice residence admissions, while comprising 25 per cent of the national youth population".

Wiffin said the country had learned nothing. "In the institution I was in, for example, 70 per cent Māori".

"It's a crime in itself."

Wiffin said this research itself, outside of the inquiry's interim report, showed a need for change. "I'm looking into the future and hoping that the final report, in conjunction with a far more critical analysis, will have some strong recommendations which will bring about fundamental change in terms of attitude and approach."