Statistics New Zealand has asked two independent experts to review the low turnout for this year's census, which followed a 'digital first' model.

Fewer New Zealanders than expected completed this year's census after the process was moved online, Stats NZ confirmed earlier this year.

Statistics New Zealand received full or partial information for at least 90 percent of people from this year's census, compared with 94.5 percent during the last census in 2013.

It has now called on the services of management consultant Murray Jack and Canadian census expert Connie Graziadei, who has recently retired as assistant chief statistician in her own country, to review the turnout.

Government Statistician Liz MacPherson said the agency has asked the pair for a final report by next July.

"We want to know what worked well and what did not work well, and why. We need to be clear about what we should have done better."

She said she was sure Mr jack and Ms Graziadei would "leave no stone unturned".

"We know how important census information is for decision-makers across New Zealand, and so it is vital that we maintain public trust and confidence in the census. I'm determined to do that, and the independent review, as well as the external data quality panel, announced in early September, are key steps on the way," Ms MacPherson said..