An analytical paper published by the NZ Treasury last week raises questions about the accuracy of migration figures, largely because of the hard-to-analyse internal migration.
The paper’s author, senior Treasury modelling analyst Keith McLeod, said in its introduction: “Our estimate of Auckland population growth due to net migration between 2013-16 is about half the official figure.”
The paper describes new sub-national New Zealand population measures that Treasury has developed using integrated administrative data. They’re in an interactive online form in Treasury’s Insights tool.
The paper doesn’t accuse others of getting things wrong – and Treasury says of its own work that it can’t be trusted yet. It’s more a case of additional information giving a more accurate picture of population movements.
Mr McLeod: “New Zealand has a robust system of population estimates, and the data described in this paper has the potential to complement this system. Nevertheless, the results are exploratory in nature, and further work is required to better understand the strengths & limitations of the data. The findings are not official statistics and should be treated with caution.
“A particular strength of the analysis outlined here is the ability to measure & describe patterns of internal migration within New Zealand, something that has previously been largely reliant on the 5-yearly census.
“The analysis not only describes patterns of internal migration, but sets these alongside other key dimensions of population change: ageing, natural increase & international migration.”
Estimates aren’t immediately available for release, and results for a particular calendar year are only likely to be able to be produced 9 or more months after the end of that year.
The Auckland question
On the question of Auckland’s growth, the paper says: “Auckland, New Zealand’s largest city, has experienced year-on-year growth since 2008. This has been driven largely by migration from overseas, with foreign migrants more than offsetting net losses of New Zealanders moving away.
“Since 2012, increasing numbers of people have been leaving Auckland to move to other areas, especially Tauranga, Waikato District, Whangarei & the Far North. This has slowed population increase in Auckland over that period.
“Although the case studies presented here tell a similar story to official population estimates, there are some differences, particularly in Auckland, where our estimates show much lower population growth in recent years.
“Our estimate of Auckland population growth due to net migration between 2013-16 is about half the official figure.
“More work is required to better understand these differences. The difference could derive from the difficulty in determining people’s location of residence after their arrival in New Zealand in either or both of the sources, or may relate to the different residence definitions adopted.”
- For me, this research is very welcome because information on internal migration has long appeared to be lacking.
Treasury Insights analytical paper, 18 April 2018: Where we come from, where we go – describing population change in NZ
Attribution: Treasury Insights.