Police have been accused of presenting crime statistics in a way which could unwittingly identify the individuals involved.
Photo: RNZ / Alexander Robertson
In November 2016 police took over the reporting of crime data from Statistics New Zealand.
But documents obtained under the Official Information Act show how concerned Statistics New Zealand officials were with the way police were handling the data.
One wrote in an email: "Police in this case are seeking to release a series of substantively personal government-held data and information tables, in a manner which does not seem to appropriately protect personal, confidential and classified data and information."
Another talked about Statistics New Zealand agreeing to an option that would avoid Government Statistician Liz MacPherson having to approve "either explicitly or implicitly" what police were doing.
Police are refusing to perturb the crime data, or round small numbers up to ensure anonymity.
Andrew Balemi, from Auckland University's statistics department, said Statistics New Zealand had every reason to be fearful of what police were doing.
"It's very, very dangerous - it can be easily politicised... or something clumsy can happen.
"Imagine if someone has been accused of paedophilia and they're innocent and they're targeted, and if that person could be isolated to within a geographical region... what a nightmare," Dr Balemi said.
The police should stick to solving crime, he said.
Labour police spokesperson Stuart Nash said any concerns raised by Statistics New Zealand should be taken seriously.
"Goodness me, if Stats New Zealand have a problem then I think we should all be concerned about that.
"These guys know what they are doing and they know how to do this stuff well."
Police said what they were doing was safe.
Acting deputy chief executive of strategy Mike Webb said perturbing crime data at a local level made it less useful.
"If there's say one burglary in your street last month, that might be a matter that concerns you a bit.
"But the difference around perturbing data [is it] would actually report that one burglary in your street as a three, because the numbers are too low so the perturbing disciplines kick in."
He said that would mean people would misread the situation and it would negatively affect their fear of crime.
Mr Webb said police were using some data suppression techniques and had struck the right balance.
"There were some concerns around the level at which some of that data would be available because we didn't want to be breaching people's privacy - particularly around some of the more sensitive and low-volume crimes," Mr Webb said.
"But we're really happy with the way in which we worked through [that] with Stats New Zealand and benefited from guidance from the Office of the Privacy Commissioner."
Government Statistician Liz MacPherson did not respond to RNZ's requests for an interview.
But in October she wrote to Police Commissioner Mike Bush, saying: "I appreciate that you have carefully assessed and are prepared to accept any residual risk associated with the proposed reports, as highlighted by Statistics NZ's confidentiality experts."
In a statement, the Statistics New Zealand media team said the problems that were identified had been resolved but would not specify how that had happened.