Net Internal and International Migration
These maps are based on the Estimated Resident Population Count (ERP). Numbers and percentages for Net Internal Migration thus differ slightly to counts based on Census Usually Resident Population (CURP).1
These maps provide an indication of the relative percentage contributions of net internal migration, net international migration and total net migration to the Estimated Resident Population of each territorial authority area in each census year. The data to 2013 are drawn from the MBIE-funded project 'Nga Tangata Oho Mairangi' (NTOM) (The Impact of Demographic Change on New Zealand's Communities) led by researchers at Massey University, the University of Waikato, and Motu between 2012 and 2014 http://www.ngatangata.ac.nz/massey/learning/departments/centres-research/ntom/ntom_home.cfm. The data were generated by Professor Natalie Jackson and Ms Shefali Pawar of NIDEA (National Institute of Demographic and Economic Analysis) via the development of a Demographic Accounting Model. Data for the period 2013-2018 have been generated by Jackson and Pawar using the same methodology.
The Demographic Accounting Model applies a step-wise process to Statistics New Zealand data on births, deaths, internal arrivals and departures and population counts, to generate, as a residual category, a value for net overseas migration.
- First, for each area, deaths are subtracted from births to generate natural increase (and natural decrease where it occurs).
- Second, natural increase is subtracted from net population change (Estimated Resident Population, ERP) to generate total net migration as a residual measure.
- Third, using Census Usually Resident Population Counts (CURP), internal departures from each area are estimated and subtracted from internal arrivals to each area, to generate values for net internal migration (see ‘Mover-Stayer’ methodological notes below).
- Fourth, net internal migration at CURP level is raised to Estimated Resident Population level by applying the ratio of ERP to CURP in each census year, for each area.
- Fifth, net internal migration is subtracted from total net migration to generate net overseas migration as a residual.
- Overseas departures can also be estimated from this process, by subtracting overseas arrivals to each area from net overseas migration—however the result is at best a crude approximation.
Demographic Accounting Methodology (Summary)
- 1. Deaths are subtracted from Births to generate Natural Increase (ERP level)
- 2. Natural Increase is subtracted from Net Change to generate Net Migration (ERP Level)
- 3. Internal Leavers are subtracted from Internal Arrivals to generate Net Internal Migration (CURP level)
- 4. CURP Net Internal Migration is raised to ERP level by applying the ERP:CURP ratio
- 5. Net Internal Migration is subtracted from Net Migration to generate Net Overseas Migration (ERP level)
- 1. [There are three main population counts. The Census Night count pertains to all people counted in each area on Census Night. The Census Usually Resident Count (CURP) has reallocated people to their usual residence based on postcode, and removed overseas visitors. The Estimated Resident Population (ERP) count is released quarterly and includes adjustments for births, deaths and migration occurring since the previous census.]↩
Census Usually Resident Population Counts (CURP) were originally sourced from Statistics New Zealand (2014, 2020) and are based on the Census question ‘where did you usually live five years ago?’ Because some people fail to provide this information on their census form, a methodological decision was made to prorate the data for those people according to the local (regional or territorial authority area) distribution for those whose address five years ago was stated (see caveat below).
Data for people who gave both their current and past address were categorised as either:
- Stayers (people living in the same region or territorial authority area at both censuses—although they may have moved elsewhere within that area, and/or out of the area and back in, between the censuses);
- Internal Arrivals (people living in the specified region or territorial authority area who lived elsewhere in New Zealand five years ago);
- Internal Departures (people who lived in the specified region or territorial authority area five years ago, but now live elsewhere in New Zealand);
- Overseas Arrivals (people who were living overseas five years ago); or
- Not Born Five Years Ago (children aged 0-4 years, born since the previous census and whose address five years ago cannot therefore be determined).
Those who did not provide their current and/or previous address are recorded at the various censuses as either 'living elsewhere in NZ/not further defined', 'not elsewhere included/address five years ago not stated' or ‘unable to match’ (hereafter ‘Unmatched’. Unmatched data were prorated across ‘known’ migration as follows:
Stayers in each region or territorial authority area, Arrivals from each other region or territorial authority area, and Arrivals from Overseas were summed and their distribution calculated as a percentage. This percentage was then applied to the ‘unmatched’ number and the resulting number added to the number having stated their previous residence.
Leavers. The database is set up as a matrix, with area of usual residence 5 years ago juxtaposed against area of usual residence at each census. The resulting (prorated) Internal Arrival numbers to each territorial authority or regional council area simultaneously become Internal Leavers from those areas, based on their address 5 years ago.
Caveat: The methodological assumption that people who ‘lived elsewhere in New Zealand/not further defined’, ‘not elsewhere included/address five years ago not stated’ or ‘unmatched’ have the same mover-stayer distribution as those who did specify their previous address may be incorrect. We took this approach because it is preferable to calculating movements based on ‘known’ previous residence only, as these proportions differ substantially for each region and territorial authority area. The resulting data should thus be viewed as a best approximation of the situation and will differ slightly from the raw data that Statistics New Zealand publishes, and other analysts may generate.
- Mover-Stayer Methodology (Summary)
- 1. TA/RC of usual residence (time t+5) by TA/RC of usual address five years ago (time t) are juxtaposed in a matrix
- 2. Stayers, Internal Arrivals, and Overseas Arrivals are summed and their % distribution calculated
- 3. Not Specified/Inadequately defined/New Zealand not further defined/unable to match are prorated
- 4. Prorated data are added to 'known' Stayers and Movers
- 5. Internal Arrivals (prorated) = the sum of Arrivals from all other TA/RC areas (CURP at t+5 years minus Stayers),
-     Internal Leavers (prorated) = Sum of Usual Residence at time t minus Stayers
- 6. Net Internal Migration at time t+5 = Net Internal Arrivals minus Net Internal Departures
Statistics New Zealand (2020) Customised Database, Area of Usual Residence (2018) and Usual Residence 5 Years Ago (2013) by Age Groups for the Census Usually Resident Population Count 2018
Statistics New Zealand (2014) Customised Database, Area of Usual Residence (1996, 2001, 2006, 2013 and 2018) and Usual Residence 5 Years Ago (1991, 1996, 2008 and 2013) by Age Groups for the Census Usually Resident Population Count, 1996, 2001, 2006 and 2013.