Subnational Population Estimates (2013-base)

Subnational population estimates The estimated resident population for subnational areas by age and sex at 30 June are produced annually. First release of provisional subnational population estimates at 30 June of a reference year generally become available in October of the same year. Following the availability of a new Census-based estimated resident population (ERP), intercensal national and subnational estimates are revised to incorporate the new ERP. Geographic boundaries From November 2018, we have published population estimates based on the Statistical standard for geographic areas 2018 which includes new statistical geographies such as statistical area 2 (SA2) and urban rural. Estimates are available at regional council (regions), territorial authority (TAs), Auckland local board (ALBs), urban area (UAs), district health board (DHBs), area unit (AUs), and other local government geographies, including wards, community boards, constituencies, and subdivisions. Population estimates by other geographic areas can also be produced on request. Subnational estimates are released on the most recent published boundaries (at 1 January of the reference year). From October 2019, we have discontinued producing population estimates using area units (replaced by SA2). These will be available as a customised job. Base population The estimated resident population at 30 June 2013 forms the base population for deriving current post-censal population estimates. The estimated resident population of each area at 30 June 2013 is based on the census usually resident population count from the 2013 Census (held 5 March 2013), with adjustments for: people missed or counted more than once by the census (net census undercount), residents temporarily overseas on census night, births, deaths, and net migration between census night and 30 June 2013, reconciliation with demographic estimates at ages 0–9 years. 2013-base territorial authority and Auckland local board (TALB) estimates TALB estimates are derived using a component method. They are based on the latest Census data and updated to account for births, deaths, and net migration since the Census. The formula used for estimating the resident population in each TALB is: Population (current year) = population (previous year) + births - deaths + net internal migration + net international migration. All components of the formula (on the right-hand side of the equation) are estimates of the number of events that occurred during the current year ended 30 June. The estimates are constrained to agree with the corresponding national estimated resident population at the time of publication. Births/Deaths Birth and death registrations are used to estimate the number of births and deaths that occurred during each June year. There is often a delay between when a birth or death occurs and when it is registered, and this delay is accounted for when estimating birth and death occurrences. Net migration For subnational areas, net migration includes net gains from international migration (flows into and out of New Zealand) and net gains from internal migration (flows between areas in New Zealand) during the June year. Annual international and internal migration flows are estimated as two different processes. Multiple administrative data sources are traditionally used to derive estimates of subnational migration because: there is no direct measure of internal migration in New Zealand other than the periodic Census of Population and Dwellings, the direct measure of international migration (via the outcomes-based migration measure) will use integrated address information from administrative data to inform the geographic distributions of the international migration estimates when estimates are final. International/external migration Since 2004, Statistics NZ has implemented several changes to its estimation methods aimed at improving the accuracy of population estimates. This has included the use of new data sources and refined methods for using existing data sources. These initiatives have been given greater impetus due to: the estimation challenges raised by the 2010/11 Canterbury earthquakes, the cancellation of the 2011 Census of Population and Dwellings, resulting in population estimates extended further out from the 2006 base population. For annual updates to subnational population estimates in the 2013–18 period, we primarily used three data sources to estimate subnational migration by age and sex: international (permanent and long-term) migration statistics, primary health organisation (PHO) enrolment data, Inland Revenue (IR) tax data. The three datasets had high rates of population coverage, including the key demographic variables of age and sex, and captured information on geographic locations. In using these three data sources, efforts were made to identify and make use of their respective strengths. With regards to estimating subnational migration by age: international migration data to estimate international migration by age and sex, PHO data were used to estimate internal migration for the population aged 0–14 years and 45 years and over, IR tax data were used to estimate internal migration for the population aged 25–44 years. Several additional data sources were used to validate the estimates. They included: electoral enrolment data, residential building consents, information provided by territorial authority areas during annual consultation, data on specific population sub-groups, namely defence force personnel, prison populations, and tertiary students. See Summary of changes to Subnational population estimates: At 30 June 2019 (provisional). 2013-base area unit methods* From 2013, area unit (or Statistical Area 2 from November 2018) population estimates have been derived using proportions derived from administrative data sources as a means of apportioning out the TA population to the AUs/SA2s within each TA. The proportion of the TA population assigned to a particular AUs/SA2s is determined using a combination of administrative sources including primary health organisation (PHO) enrolment data, electoral enrolment (EEC) data and Inland Revenue (IR) tax data, as well as the previous year AUs/SA2s population estimates. Birth registration data are also used to determine proportions for those aged under one. A different combination of these sources is used to determine an apportionment factor (the proportion of the TA population to be assigned) for each AUs/SA2s age/sex group. For each AUs/SA2s and age/sex group, the combination of data sources used to determine the apportionment factor varies depending on their suitability for estimating the population for that area and age/sex group. For example, electoral enrolment data was only used to help determine apportionment factors for those of voting age. Previous area unit methods Until 2013, Statistics NZ produced area unit population estimates using a component methodology, where the components of population change (births, deaths, and migration) are used to update a base population. The formula used for estimating the resident population in each area unit was: Population (current year) = population (previous year) + births - deaths + net migration (internal and external/international migration combined). Occurrences of births and deaths were estimated using information from birth and death registrations (available at the AU level). In contrast, information relating to net migration was not readily available at the AU level. For this reason, the net migration component required a special estimation methodology. Intercensal net migration estimates for AUs were traditionally modelled on the relationship between net migration and building consents during the last intercensal period (eg 2002–06), building consents during the period of interest, and occupancy rates at the time of the last census. Other salient information received by Statistics NZ, such as information from local councils during the annual consultation, was also incorporated. The initial estimate of net migration for each AU was then adjusted to sum to the net migration estimate for each TA. During 2011, following the 2010/11 Canterbury earthquakes, various data sources were used to assess subnational migration for earthquake-affected AUs in Waimakariri district, Christchurch city, and Selwyn district, including PHO enrolment data, taxation data from the Linked Employer-Employee Dataset (LEED), dwelling assessments by the Earthquake Commission, and electricity consumption data. During 2012, data sources used for producing subnational migration estimates at 30 June 2012 were further evaluated and a similar method used for TAs was applied for AUs. There were challenges associated with estimating subnational migration between each AU, as international migration data are not available at the AU level. This component was generated by apportioning out the total TA net migration gain/loss amongst the AUs. These methods have now been superseded by the apportionment method described in 'Current area unit methods' above. Rounding All published figures are calculated using data of greater precision. Individual figures may not sum to totals due to rounding. The rounding of estimates of the five-year age groups, broad age groups, and total all ages is determined by the total population size of the geographic area. Five-year age groups For areas with a population less than 2,000, estimates are rounded to the nearest 5. For areas with a population of 2,000 and more, estimates are rounded to the nearest 10. Broad age groups and total all ages For areas with a population less than 10,000, estimates are rounded to the nearest 10. For areas with a population between 10,000 and 20,000, estimates are rounded to the nearest 50. For areas with a population of 20,000 or more, estimates are rounded to the nearest 100. The rounding of estimates of natural increase, net migration, and population change is determined by the size of components. For components have an absolute value less than 1,000, estimates are rounded to the nearest 10. For components have an absolute value of 1,000 or more, estimates are rounded to the nearest 100. en-NZ