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Subnational Population Estimates: At 30 June 2015 (provisional)
Embargoed until 10:45am  –  22 October 2015
Data quality

Period-specific information
This section contains information about data that has changed since the last release.

General information
This section contains information that does not change between releases.

Period-specific information

Data sources used to estimate subnational migration

For the year to 30 June 2015, we used both traditional and new data sources to estimate subnational migration.

For subnational areas, net migration includes international migration (flows into and out of New Zealand) and internal migration (flows between areas in New Zealand). Multiple 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
  • while New Zealand does have a direct measure of international migration (via the arrival and departure cards completed by passengers), vague, incomplete, and temporary addresses affect the quality of geographic information.

While producing subnational population estimates at 30 June 2015, we primarily used three data sources to estimate subnational migration by age and sex:

  • international (permanent and long-term) migration statistics
  • primary health organisation enrolment data
  • Inland Revenue tax data.

We selected these three datasets because they have high rates of population coverage, include the key demographic variables of age and sex, and capture information on geographic location.

In using these three data sources, we aimed to identify and use their respective strengths. With regards to estimating subnational migration by age, we used:

  • international migration data to estimate international migration for all ages
  • primary health organisation enrolment data to estimate internal migration for the population aged 0–14 years and 45 years and over
  • Inland Revenue tax data to estimate internal migration for the population aged 25–44 years.

There are particular challenges associated with estimating subnational migration for the 15–24-year age group. Not only is this group highly mobile, it has low coverage in many datasets (including primary health organisation enrolment data and Inland Revenue tax data). As a result, we estimated subnational migration for this age group using the information sources mentioned above, as well as historical estimates and age-sex net migration patterns derived from population projections.

Once we created preliminary estimates of subnational migration, we used several additional data sources to validate the estimates. The information sources used to validate the estimates included:

  • electoral enrolment data
  • residential building consents 
  • information provided by territorial authorities during the annual consultation
  • data on specific population subgroups; namely defence force personnel, prison populations, and tertiary students.

See Evaluation of alternative data sources for population estimates and Evaluation of administrative data sources for subnational population estimates for additional information on the data sources mentioned in this section.

International migration for Auckland local board areas

We process information on permanent and long-term migration by New Zealand area at the territorial authority level. Due to the large size of the Auckland territorial authority, we need a way to assign international migration across Auckland.

Using information from the Integrated Data Infrastructure (IDI), we have derived a historical distribution of permanent and long-term arrivals and departures by age and sex for the 21 Auckland local board areas. Total arrivals and departures into Auckland for the June 2015 year were then distributed across the local board areas according to these historical results.

Geographic boundaries

The population estimates in this release are based on boundaries at 1 January 2015.

Provisional and final estimates

The population estimates contained in this release are provisional. They incorporate provisional estimates of births and deaths that occurred in the June 2015 year. 

Final estimates will be released on 18 November 2015. We derive these final estimates when an extra quarter of births and deaths data is available.

General information

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. 

Deriving subnational population estimates

We derived subnational population estimates for dates after 30 June 2013 by updating the estimated resident population of each area at 30 June 2013 for births, deaths, and net migration (international and internal migration combined).

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 taken into account when estimating birth and death occurrences.

We use multiple data sources to derive estimates of subnational migration.
See Data sources used to estimate subnational migration.

Subnational population estimates are consistent with national population estimates for a given reference date.

Nature of estimates

Population estimates give the best available measure of the size and age-sex composition of the population usually living in an area. However, uncertainty is inherent in the estimation process.

Statistics NZ produces subnational population estimates using a component methodology, which uses the components of population change (births, deaths, and net migration) to update a base population. There is some uncertainty associated with component data, particularly the estimation of net migration (international and internal migration combined) for subnational areas. Generally speaking, the uncertainty associated with population estimates increases as the estimates move further away from the base (starting point). Uncertainty also increases as population estimates are broken down by age, sex, and geographic area.

In reality, no data source perfectly measures the resident population of New Zealand or of subnational areas. Furthermore, no data source perfectly measures changes in the resident population, or even movements of the resident population within New Zealand.

The periodic Census of Population and Dwellings remains the cornerstone of population statistics in New Zealand. Following the 2013 Census we have derived updated estimates of the population, to assess the accuracy of estimates since 2006, and to revise estimates where necessary.

Data accuracy

We cannot ascertain the accuracy of current population estimates as no independent authoritative measure of the resident population exists. Since 2006, we have implemented a number of changes to our estimation methods, aimed at improving the accuracy of population estimates. This included using new data sources and refining methods for using existing data sources. See Data sources used to estimate subnational migration.

Rounding

All figures in this release are rounded independently. All derived figures in this release are calculated using data of greater precision than published.

The rounding of estimates of the total population, and broad age groups, is determined by the total population size of the geographic area. Estimates for areas with a population less than 10,000 are rounded to the nearest 10. For areas with a population between 10,000 and 20,000, estimates are rounded to the nearest 50. Estimates for areas with a population of 20,000 or more are rounded to the nearest 100. The rounding of estimates of natural increase, net migration, and population change is also determined by the total population size of the geographic area.

More information

Information about the population estimates contains detailed information about the methods used to derive population estimates.

Statistics in this release have been produced in accordance with the Official Statistics System principles and protocols for producers of Tier 1 statistics for quality. They conform to the Statistics NZ Methodological Standard for Reporting of Data Quality.

Liability 

While all care and diligence has been used in processing, analysing, and extracting data and information in this publication, Statistics NZ gives no warranty it is error-free and will not be liable for any loss or damage suffered by the use directly, or indirectly, of the information in this publication.

Timing of published data

Our information releases are delivered electronically by third parties. Delivery may be delayed by circumstances outside our control. Statistics NZ does not accept responsibility for any such delay.

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