The 2018 census had the worst participation rate in New Zealand since post World War Two.
There are 400,000 people missing from the results of this census.
National spokesman for state services Nick Smith told Chris Lynch in Nelson he had retirement homes ringing and saying they had one packet for 100 residences, and it was the same with student university halls.
"They've got over 400,000 people from their census data, so what they intend to do is take the census data from 2013 and attempt with computer modelling make up for those 400,000 people that they didn't count."
Planning for the census started under the National Government, but Smith says that National increased the budget for this census from 2013.
He puts the blame squarely on Minister for Statistics James Shaw, and says he should have been in the country making sure it ran properly.
LISTEN TO NICK SMITH TALK WITH CHRIS LYNCH ABOVE