Tatau tātou, eh?

According to the Herald, the government has decided to stop doing the Census after the next (2028) round and switch to yearly administrative data from 2030.  The press release is here, and StatsNZ’s page is here.  There’s no commitment so far to get the necessary legislative changes passed before the election, but that may come.

This was inevitable at some point.  Door-to-door enumeration is getting less effective and administrative data are getting more complete: eventually the two lines will cross. There are quite a few countries that have more detailed and thorough government data collection than us and don’t bother with censuses. They get on fine. I’m not sure we’re there yet, but maybe we will be in 2030?

At the crude level of “how many people are there and roughly where do they live and what work do they do?”, administrative data is great.  The use of administrative data in the 2018 and 2023 Censuses improved the counts of people by region, and especially improved the counts for Māori.  There are some important weaknesses, though.

First, the `administrative’ data used to augment the 2018 and 2023 Censuses included past Census data, not just routinely-collected government data.  In 2018, the first-priority source for additional data was the 2013 Census, and it was often important. For example, when creating the “Māori descent for electoral purposes” variable, StatsNZ found 15% of the “Yes” values and 7.7% of the “No” values in 2013 Census data. [Table 4.2, Initial report of Census data quality panel].  If we stop doing Censuses, the existing Census data will rapidly become less useful.

Second, administrative data is much less effective for household statistics than for individual statistics.  Most routine government data collection is about individuals.  If Chris reported a particular Auckland address in March 2025 and Pat reported that address in December 2024 and Sandy reported it in July 2024 and Alex in June 2024, how do you work out which subset of these folks were ever living there together? And that’s before you get to situations like if you’ve just started flatting but your doctor has your Mum’s address and your boss has your Dad’s address.   In 2018, household data were a big weakness of the Census — nearly 8% of the census population didn’t have an assigned household. StatsNZ did a lot of work on this subsequently, but it’s hard.

Third, there are data that just aren’t collected routinely. Iwi affiliation, disabilities, and housing quality variables were examples from 2018. If these variables are wanted, they will have to be collected in other surveys, and there’s no clear reason to expect the other surveys to be more accurate than the Census. In particular, they may have worse non-response rates for Māori and for minority groups.

There’s also a potential social license issue.  People understand the Census and have some idea of what it’s for, and mostly approve.  The IDI is much less well understood, and I think is less popular. Replacing the Census with surveys and vacuuming up of data collected for other purposes could well have a negative effect on public willingness to give up their data and public trust in the results.

Good sources if you want to read about this include the StatsNZ page, whatever Len Cook writes, and also the reports of the 2018 Census Data Quality Panel (there’s a 2023 report, but it’s much smaller and mostly talks about minor improvements in methods).