Statistics Minister James Shaw has fired a blistering broadside at the Opposition leader, accusing Simon Bridges of undermining public trust in statistics in a win-at-all-costs "burn-the-house-down" approach to politics.

Photo: RNZ / Dom Thomas

But Mr Bridges is doubling-down on his questioning of Statistics New Zealand's figures and says Mr Shaw - who's also Green Party co-leader - is lashing out under pressure.

The National leader yesterday told RNZ's Morning Report he questioned the credibility of Stats NZ and its work after a damning review laid bare significant data gaps in the 2018 census and, separately, migration and growth figures had to be revised.

Mr Shaw said Mr Bridges' position was "desperate" and "completely irresponsible".

"Stats NZ - their success ratings for the information that they put out on a weekly basis is between 99 percent and 100 percent ... and when they do have errors, they correct them, they publish the methodology, they get them third-party reviewed.

"The idea that you can say, 'Oh, they made a mistake over here, therefore, I don't trust anything that they've produced', I think is, frankly, absurd."

The Opposition had a strategy to undermine public confidence in statistics in a bid to retake power "at any cost", Mr Shaw said.

"The lessons of Trump, the lessons of Brexit, and the lessons of the Australian election seem to have gone to Simon Bridges' head and this 'burn-the-house-down' in order to win approach ... is a very, very bad turn for New Zealand politics.

"He doesn't really care what the collateral damage is along the way ... and I don't know how he expects to govern if he totally destroys public confidence in the basis of evidence-based decision making."

Photo: RNZ / DOM THOMAS

Mr Bridges told RNZ he stood by his comments and said it was his duty as Opposition leader to ask tough questions on behalf of the public.

"After a botched Budget - which there's no denying - and after we've had wild variation in a number of statistics, I think these are things for [Mr Shaw] to satisfy the public on."

Mr Bridges said the minister's personal attack showed the pressure was getting to him.

"James Shaw was asleep at the wheel and we had a botched census delivered," Mr Bridges said.

"What you've got is a co-leader who's lashing out in a pretty bizarre way, because he's rattled, and he - and his coalition partners - are under pressure."

Mr Bridges told RNZ he did not accept Stats NZ's assurances that the figures used to determine electorate boundaries would be robust.

"We've got significant numbers of New Zealanders - hundreds of thousands in fact - who weren't counted. It seems to me on that basis, it would be hard to run new electoral boundaries."

But Mr Shaw said the census work had been overseen and approved by "an independent data quality review panel".

"Experts from all over the country - including someone from the UK Statistical Office as well to provide that international view - and they have put the gold stamp on this."

And Mr Shaw challenged Mr Bridges to test the results in court: "He can take it into a court of law if he likes, but he's going to lose."

Independent economist Brian Easton said Mr Bridges was "premature" to dismiss aspects of the census outright.

"We haven't actually seen the data, so we can't jump to conclusions," Mr Easton said.

"What we've got is people who are uninformed who are panicking - and quite illegitimately. What they've got to do is wait and see what happens."

Mr Easton advised critics to wait for the release of the first census information on 23 September before criticising it.

"I respect Mr Bridges saying that if they don't have the confidence in the data, then we should stay with the 2013 electoral boundaries.

"But how will he know that until he's seen it?"

Mr Easton said he had "considerable confidence" in New Zealand's statisticians and the quality of their work, but Stats NZ's management had been overly optimistic.