Massey University's pro vice-chanceller has added his voice to calls for Statistics New Zealand to "front" on the "failed" 2018 Census.
Last year was the first online Census, switching away from paper forms, and Statistics New Zealand has reported a much lower-than-expected response rate, as well as many incomplete forms.
Work has been done since July last year to understand why, Stats NZ has said.
National Party Leader Simon Bridges yesterday said he is losing faith in the agency after it refused to give Parliament answers on why releasing the data is taking so long
A notice on the Stats NZ website reads: "Stats NZ will provide an update in April 2019 about the release of 2018 Census data.
"It always takes time for us to analyse and produce the dataset, but this time, we are taking longer than usual because the overall individual response was lower than we had aimed for.
"We are filling in information missing from 2018 Census using other government data about real people, (such as births, tax, health, and education records)."
Speaking this morning to TVNZ1's Breakfast programme, Massey University Professor and Pro Vice-Chancellor Paul Spoonley said he also thinks it's time for Stats NZ to "come clean".
"I really would like the chief statistician, Liz MacPherson, to be honest with us ... I think the parliamentarians are rightly getting really annoyed that she isn't being upfront about the failure of the 2018 Census," Mr Spoonley said.
"A lot of our systems, our institutions rely on it - our funding for education and health relies on it - so we need that database on the population to determine DHB funding, for example.
"We've got an election coming up next year - normally by this time, the review of electorate boundaries would have been done - it would have been announced in March this year for a 2020 election.
"We still do not have the Census data in order to look at the electorate boundaries and where any new electorates should be or where electorate boundaries should be changed.
"So a whole lot of systems are actually breaking down because we don't have Census data available."
Mr Spoonley said he believes it was wrong to switch to an online system without testing it.
"What went wrong is we went online with a system that we really hadn't tested - so I would have kept the old system, which had people turning up at your door and saying, 'Here's the Census, here's why you need to fill it in, and I'm coming back.'
"And there were a whole lot of people who were not able to access the data online, and unfortunately the numbers involved are quite significant for groups that we need to know about."
Mr Spoonley said a colleague of his had estimated that the issue could disproportionately affect Māori populations, especially in the Northland and East Coast areas.
"For some Māori it might be as low as 70 to 80%...so if we're looking at policies and looking at funding, that sort of shortfall is huge.
"It's based on a population funding model - so you need to know what your population is."
He said Statistics New Zealand are "backfilling" missing data from other sources, but that leaves the serious question of whether New Zealand can have confidence that the replacement data will be correct.
"I'm still very, very sceptical."
Mr Spoonley called out Stats NZ's MacPherson, who has delayed releasing any data four times now.
"This is a public agency - it's really important to this country. It provides something of value, around a billion dollars, to this country.
"I think Liz MacPherson does need to front."