The 2018 Census data will be more accurate than that in the previous census, Statistics Minister James Shaw says.
Yesterday, Stats NZ announced it had plugged enough of the gaps in last year's census using a method that combines 89 percent of real census data and 11 percent of other government administrative data.
It said it would start releasing data from September after a low response rate delayed the data release twice.
Mr Shaw told Morning Report ACC was one of the pools of government data that the census had pulled from to help complete the population count.
"For example, ACC will have records about real people and what their address is, and if someone didn't fill out and a census form, well we still have that information that someone exists at this address and so we've combined what we know about the population with the census forms."
Mr Shaw said the compiled population count was more accurate than the previous census, because they were able to use other sources.
"The data we've got about the population count does appear at this point to be more accurate than it did in the 2013 Census."
However, some of the details of population counts might be missed when taken from administrative data, Massey University Professor Paul Spoonley told Morning Report.
"When you get down to some of the details particularly around households, people in those households, the characteristics of the people in those households, no, it's not going to be as good as the last census," Prof Spoonley said.
"There's only certain sorts of data that are going to be collected [from government systems], so the question is what's left out and what therefore is not going to be available for the census?"
Prime Minister Jacinda Ardern told Morning Report there would be some gaps but that Stats NZ has given assurances that for those things that were critical to the work of government, in health and education, they'd have what they needed.
"We have been given the reassurance by Stats NZ that it estimates it has records for 4.7 million people, it's population data is robust enough to do important things that we rely on."
On the other hand, National's statistics spokesperson Jian Yang told Morning Report there were still some concerns about the timeliness and a lack of first-hand information from the Census itself.
"We encourage the government to somehow move the next census ahead because by the time they finish releasing [this] census' data, it will be outdated," Mr Yang said.
"Looking at this census cycle from 2001 and 2006, over half of New Zealanders moved their residence during that five years, so two-and-a-half years is a long time [to be waiting for the data release], by then the census data may be outdated already."
Mr Yang said the census was "very poorly organised, very chaotic" and criticised Mr Shaw over a lack of interest.
"You'll find that the access code was sent out very late and many people did not have an access code 'til very close to census day or after census day and then people would need to request paper forms but when they called the 0800 number, they couldn't get through.
"Minister Shaw did not really show much interest in Census 2018, he didn't publish any media release, only one single press release, not encouraging people to participate but to complain about the content of the census, while in sharp contrast, in the final months leading to the 2013 Census, the minister at the time published seven press releases encouraging people to participate."
At the time, the minister was heavily criticised by the opposition for not being present in the country on census day. Mr Shaw, who is also the Climate Change Minister, was with Ms Ardern on her first trip to the Pacific region as prime minister.
However, Mr Shaw said his presence would make no difference in the outcome and added that the difficulty in participation might have something to do with the changing census model.
"It appears at this point is that the difficulty was they were changing their ground model and it didn't get out to all the households that it needed to."
As a result, some sublevel data was less accurate than anticipated, Mr Shaw said.
"The piece around iwi affiliation is particularly disappointing," he said.
"So the iwi affiliation data is going to get released, but it won't have the official stamp, if you like, of statistics because they are not confident that it quite gets the level of quality that they would like it to be able to release it as an official statistic."
He said the census team was working with data iwi leaders group to make sure they were able to use that information and how they could improve it in the future.
The low turnout has also sparked a review into the census, conducted by an independent panel, and Mr Shaw said he would be taking a strong steer in making sure it doesn't happen again.