Demographic Estimates

Census usually resident population count A count of all people who usually live in a given area and are present in New Zealand on a give census night. This count excludes visitors from overseas, visitors from elsewhere in New Zealand, and residents temporarily overseas on census night. The population counts published from the census are not comparable with the estimated resident population. Estimated resident population An estimate of all people who usually live in an area for 12 months or more at a given date. Visitors from elsewhere in New Zealand or from overseas are excluded. Estimated de facto population the estimated de facto population of New Zealand includes all people present in New Zealand and counted by the census (census night population count). This estimate includes visitors from overseas who are counted on census night, but excludes New Zealand residents who are temporarily overseas. Base population The estimated resident population at 30 June 2013 forms the base population for deriving 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 0–4 year Accuracy of the data Official national population estimates give the best available measure of how many people usually live in New Zealand. However, uncertainty is inherent in the estimation process. Stats NZ produces national population estimates using a component methodology, where the components of population change (births, deaths, and net migration) are used to update a base population. There is some uncertainty associated with the component data, particularly the estimate of the international migration. Generally speaking, the uncertainty associated with population estimates increases as the estimates move further away from the base (starting point). Uncertainty also increases as the population estimates are broken down by age and sex. Determining data accuracy It is not possible to ascertain the accuracy of current national population estimates as no independent or authoritative measure of the resident population exists. The periodic Census of Population and Dwellings remains the cornerstone of population statistics in New Zealand. Following the 2018 Census it will be possible to derive updated estimates of the population, to assess the accuracy of the estimates since 2013, and revise estimates where necessary. International migration estimates International migration statistics are based on electronic arrival and departure records supplied to Stats NZ for each international passenger. All arrivals and departures are processes so they can be allocated to one of three passenger types: overseas visitors, New Zealand-resident travellers, and permanent and long-term migrants. The net number of of permanent and long-term migrations provide the estimate of international migration used in deriving the national population estimates. Uncertainty arises due the changes in passenger intentions; a person may change their intentions after arrival or departure, which may mean the recorded passenger type becomes incorrect. Stats NZ does not revise published statistics to adjust for such changes. As a result, the uncertainty associated with the population estimates increases as the time period between the reference date of the base population and the date of the estimate increases. Net migration The difference between the number of people who have moved to, or departed from, a given area. Subnational net migration includes both international and internal migration. Internal migration Migration between areas of New Zealand Data sources used 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, and while New Zealand does have a direct measure of international migration (via arrival and departure cards completed by passengers), vague, incomplete, and temporary addresses affect the quality of the geographic information. Since 2006, Stats NZ has implemented a number of changes to its estimation methods aimed at improving the accuracy of subnational 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 and the cancellation of the 2011 Census of Population and Dwellings. which means that population estimates have to be extended further out than usual from the 2006 base (starting point). Three data sources are primarily used to estimate subnational migration by age and sex International (permanent and long term) migration statistics. address change information from primary health organisation enrolment data address change information from Inland Revenue tax data These three datasets were selected because they have high rates of population coverage, including the key demographic variables of age and sex, and capture information on address changes. 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 is used to estimate international migration for all ages primary health organisation enrolment data is used to estimate internal migration for the population aged between 0–14 years and 45 years and over Tax data from the Inland Revenue department are used 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 highly mobile, it has low coverage in many datasets (including primary health organisation enrolment data and the tax data). As a result, subnational migration for this age group is estimated using the information sources mentioned above, as well as historical estimates and age-sex net migration patterns derived from population projections. Once preliminary estimates of subnational migration has been created, several additional data sources are used to evaluate and refine the estimates. This additional process is considered necessary as no information source perfectly measures movement of the resident population. The information sources used to evaluate and refine the estimates include: school enrolment data electoral enrolment data residential building consents information provided by territorial authorities during the annual consultation data on specific population sub-groups, namely defence force personnel, prison populations, and tertiary students Birth and death estimates There is also some uncertainty associated with birth and death data. Birth and death registrations are used to estimate the number of births and deaths that occurred during each quarter. Not all births and deaths that occur in a quarter are registered by the end of the quarter, and this delay in registration is taken into account when estimating birth and death occurrences in the current quarter. Birth estimates The final estimation for births that occurred in a quarter is less accurate, as births are not registered either as closely to their occurrence as are deaths (around 5 percent of births are not registered either in the quarter of occurrence or in the subsequent quarter). The final estimation for quarterly births has a 95 percent confidence interval of ±500 (or about 3.5 percent, based on an average of 14,000 births per quarter) Death estimates The estimate of deaths that occurred in the reference quarter is taken as those deaths that were registered either in the reference quarter or in the subsequent quarter, and that occurred in the reference quarter. The provisional estimation for quarterly deaths has a 95 percent confidence interval of ±250 (or about 3.5 percent based on an average of 7,000 deaths per quarter). This final estimation for deaths is very accurate as very few deaths are registered later than one quarter after their occurrence (about 1 death in 1,000 is not). Rounding All figures are rounded independently. Estimates of the total population, natural increase, net migration, and broad age groups are rounded to the nearest 100. Population estimates of five year age groups are rounded to the nearest 10. Individual figures may not sum to stated totals due to rounding. The rounding of figures is determined by the total population size of the geographic area. The rounding rules that have been applied are shown below. | Total population size of geographic area | Rounding of five-year age group | Rounding of broad age group and total (all ages) | | :-------------------------------------------: | :-----------------------------------: | :-----------------------------------------------------: | | Less than 2,000 | 5 | 10 | | 2,000 to 9,999 | 10 | 10 | | 10,000 to 19,999 | 10 | 50 | | 20,000 or more | 10 | 100 | en-NZ