Statistics New Zealand may not release Census 2018 results until August 2019, and even then it might not be as robust as previous years. The delay has huge implications for decisions makers and funding considerations.

The continued threat of incomplete data has Statistics New Zealand again pushing the deadline for Census 2018 results.

Documents released under the Official Information Act show the department is planning for an August 2019 deadline, and continues to stare down a high risk it may not produce viable results.

A low turnout during Census 2018 has caused considerable pain for Stats NZ, which last week announced it would not make the third deadline it set - July 2019 - and promised to announce a release date in April.

Experts are concerned the repeatedly slipping deadlines will have a detrimental impact on planning and funding decisions to come in 2019, and the data might already be "stale".

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SUPPLIED Individual responses to Census 2018 were lower than hoped, and the results might not come until August 2019.

Stats NZ failed to count an estimated one in 10 New Zealanders in Census 2018, previously providing an interim response rate of at least 90 per cent of individuals providing full or partial information.

It was announced in June that other sources of Government data would be used to fill gaps in the results.

Both the actual number of responses received and the number of additional data for 2018 were redacted from documents, and Stats NZ declined to release them.

The documents show "high risks" Stats NZ continues to face include: the failure of methods to patch census data; census data failing to be fit for purpose, leading to "less than ideal" decisions being made; and a failure to provide information for the re-drawing of electorate boundaries.

ROSS GIBLIN/STUFF BERL chief economist Dr Ganesh Nana says Stats NZ needs to draw a line under Census 2018, set a release date and publish the best data it can.

Also described are a "severe incident", where some data fields on the census forms failed to cross over to another system and contributed to a month-long setback.

There was also a loss of around 200 records, requiring some households to be re-interviewed, and the data collated was not as clean as expected.

More than six months after switching off the online census, the department continues to test two methods of data imputation using other Government data.

"Stats NZ will use imputation methods to add to the census counts where we have sufficient evidence that a person exists but we have no administrative record or census response for them," a spokesman said on Tuesday.

To manage the unexpected work, the Stats NZ has hired an additional 11 fixed-term staff. Documents show contractors have stayed on longer than anticipated, and some are working overtime.

KEVIN STENT/STUFF National Party statistics spokesman Jian Yang said the handling of Census 2018 was abysmal. (file photo)

​BERL chief economist Dr Ganesh Nana said Stats NZ needed to "draw a line" under Census 2018.

"We all might have to put our hands together and say, 'Okay, the data won't be as rigorous and robust as previous census'. We might just have to admit that."

A standard census release would have BERL using the data intensively over a six-month period from about now, he said.

"That's clearly been put out of kilter this time around. The biggest concern for us is the timing of the data … the data is already starting to become stale."

The data was vital to decision making in local governments, and particularly in the regions where little other population data is available.

"One of the reported lowest reported response rates was from Māori, which does send a lot of warning signals in terms of the robustness and usefulness of the data which does come out."

DOUG FIELD/STUFF Pleasant Point woman Angela Mounsey told Stuff in February she found the new census system confusing. (File photo)

National party statistics spokesman Dr Jian Yang said Census 2018 had become a "shambles", and had likely missed the deadline for being used in planning Budget 2019.

"The census is a fundamental basis for funding, DHBs, schools, transport. All the funding for these departments and agencies is based on census.

"It means that next year the budget will be based on previous data. If it's further delayed, Budget 2020 could be affected."

Yang said the five-year budget of $120 million for Census 2018, granted by the previous Government, was adequate. Stats NZ had poorly chosen how to apply it.

Neither Stats NZ or Statistics Minister James Shaw were able to answer what information would be available for Budget 2019 by deadline.

DOUG FIELD/STUFF One in 10 people didn't fill out the 2018 census, a drop of 5 per cent from the last census (File photo).

STILL CONFIDENT

Shaw, who is in Poland for climate negotiations, said in a statement he remained confident Stats NZ was working hard to produce census data.

"They have been open about the challenges they are facing and are committed to working with their customers and stakeholders to manage the delay."

Shaw had spoken with other Government ministers about the delay, and said he received regular updates on progress.

He declined to commit Stats NZ to a release date for the data.

Stats NZ chief executive Liz McPherson has previously admitted Stats NZ "didn't get everything right", though the department continues to express confidence.

On Tuesday, a spokesman said: "Stats NZ is committed to delivering quality data for their customers and are working hard to ensure it is fit for purpose before they release it."

SUPPLIED In July, Stats NZ was still confident the 2018 census would deliver reliable data.

CONCERNED

Deputy Australian Statistician Teresa Dickinson offered any support the Australian Bureau of Statistics could provide in a June email, documents show.

"It's clear that there was a real disappointment with the overall response rate ... please don't hesitate for a moment to let me know and I'll mobilise whatever you need."

A Local Government New Zealand spokesman said "not having the data makes out job a bit tougher to do".

"Councils rely on the Census and other government surveys to provide wider information on our regions for planning and decision making."

Te Mana Raraunga, the Māori Data Sovereignty Network (made up of more than 100 Māori researchers and entrepreneurs), has said the response rate for Māori may be less than 80 per cent.

"For many iwi, the census is the only source of reliable socio-economic and demographic data about their people."

CENSUS BY THE NUMBERS

Five-year budget for Census 2018: $120 million

Census day - March 6, 2018

Online response - 83 per cent (exceeding target of 60 per cent)

Hand-delivered and posted census packs - 765,000, to 510,000 households

Reminder letters sent out - 750,000

Cost of independent review - $500,000

Review of Census results, once released - $85,000

Census response rates - 2001: 95 per cent, 2006: 94.8 per cent, 2013: 92.9 per cent

2018 response rate - Unknown, estimated at about 90 per cent