Stats NZ says it will not prosecute people for failing to fill out this year's census.

Census and collections operations deputy chief executive Simon Mason said it had not met the full requirements of the Act, so it felt it was unable to prosecute.

"Generally, we seek to prosecute only a small number of people - between 30 and 60 people - for refusing to take part in the census," Mason said.

"In the past, prosecutions focused on those who were threatening to census staff and those who actively encouraged others not to complete the census. Prosecutions can lead to a fine of up to $2000."

But the agency found an error in its processes; it had been too vague in its census wording.

By law, a data request must specify:

• the section of the Act the request is being made under
• the date people must respond by
• the consequence of non-compliance, for example, facing a fine or prosecution.

Mason said they accepted they needed to be more specific with respondents.

"We did not meet all the requirements of the Act in detail, and as a result have decided not to proceed with prosecutions for the 2023 Census," he said.

"We are undertaking an internal review to understand how we fell short of meeting all aspects of the legislative requirements of our new Act, to learn from it and take action to ensure it does not happen again."

StatsNZ said it had considered issuing an additional mandatory request for data, but found it was not in the public interest nor was it necessary because 89 to 91 percent of eligible people had responded on Census Day.

The decision had no impact on the quality of the 2023 Census, Mason said.

This story was originally published by RNZ