National Population Projections

PDF Data Dictionary

Series Description

Title

National Population Projections

Rights

Stats NZ

Abstract

National Population Projections provide projected populations of New Zealand, based on different combinations of fertility, mortality, and migration assumptions.

Demographic projections provide an indication of future trends in the size and composition of the population, labour force, families and households. The projections are used for community, business and government planning and policy-making in areas such as health, education, superannuation and transport. The projections, along with the assumptions for fertility, mortality and migration, are typically updated every two to three years.

Purpose

National population projections are produced to assist businesses and government agencies, in planning and policy-making. The projections provide information on the changing characteristics and distribution of the population, which are used to develop social policies in areas such as health and education. For example, the ageing population, population projections can help identify likely future service needs.

The projections are neither predictions nor forecasts. They provide an indication of possible future changes in the size and composition of the population. While the projection assumptions are formulated from an assessment of short-term and long-term demographic trends, there is no certainty that any of the assumptions will be realised.

Significant events impacting this study series

1996

Population concept for all demographic estimates, projections and indices changed from 'de facto' to 'resident'. Population estimates based on the de facto population concept (the estimated de facto population) include visitors from overseas, but made no adjustments for net census undercount or residents temporarily overseas. Population estimates based on the resident population concept (the estimated resident population) include adjustments for net census undercount and residents temporarily overseas, but exclude overseas visitors. The reference date for projections is shifted from 31 March to 30 June.

2012

For the first time, Statistics NZ applied a stochastic (probabilistic) approach to producing population projections. Stochastic population projections provide a means of quantifying demographic uncertainty, although it is important to note that estimates of uncertainty are themselves uncertain. By modelling uncertainty in the projection assumptions and deriving simulations, estimates of probability and uncertainty are available for each projection result. No simulation is more likely, or more unlikely, than any other. The simulations provide a probability distribution which can be summarised using percentiles, with the 50th percentile equal to the median.

Usage and limitations of the data

Nature of Projections

These projections are not predictions. The projections should be used as an indication of the overall trend, rather than as exact forecasts. The projections are updated every 2–3 years to maintain their relevance and usefulness, by incorporating new information about demographic trends and developments in methods.

The projections are designed to meet both short-term and long-term planning needs, but are not designed to be exact forecasts or to project specific annual variation. These projections are based on assumptions made about future fertility, mortality, and migration patterns of the population. While the assumptions are formulated from an assessment of short-term and long-term demographic trends, there is no certainty that any of the assumptions will be realised.

The projections do not take into account non-demographic factors (eg war, catastrophes, major government and business decisions) which may invalidate the projections.

Main users of the data

Statistics New Zealand, Ministry of Health, Government Planners/Local Body Planners, Ministry of Education, Consultants, Private Businesses.

Frequency
  1. Other

Information release

National population projections: 2020(base)–2073

Report

How accurate are population estimates and projections? An evaluation of Statistics New Zealand population estimates and projections, 1996–2013.

How accurate are population estimates and projections? An evaluation of Statistics New Zealand population estimates and projections, 1996–2013 evaluates the accuracy of recent national and subnational population estimates and projections.

The report focuses on estimates and projections of the total population produced and published since 1996, although earlier projections are included where practicable.

It is designed to help customers understand the accuracy of Stats NZ’s population estimates and projections relative to observed populations, the reasons for inaccuracies, and discusses current developments that may improve accuracy.

Information release

National population projections: 2016(base)–2068

Report

Experimental stochastic population projections for New Zealand: 2009 (base) – 2011

Studies

Coverage

Subjects
Population and migration

Data Collection

Name
National Population Projections

Methodology

Methodology

Method

The 'cohort component' method has been used to derive the population projections. Using this method, the base population is projected forward by calculating the effect of deaths and migration within each age-sex group (or cohort) according to the specified mortality and migration assumptions. New birth cohorts are added to the population by applying the specified fertility assumptions to the female population of childbearing age.

The stochastic approach used in the national population projections since the 2011-base projections involves creating 2,000 simulations for the base population, births, deaths, and net migration, and then combining these using the cohort component method.

These simulations can be summarised by percentiles, which indicate the probability that the actual result is lower than the percentile. For example, the 25th percentile indicates an estimated 25 percent chance that the actual value will be lower, and a 75 percent chance that the actual result will be higher, than this percentile.

Nine alternative percentiles of probability distribution (2.5th, 5th, 10th, 25th, 50th, 75th, 90th, 95th, and 97.5th percentiles) are available in NZ.Stat.

Projection Assumptions

Projection assumptions are formulated after analysis of short-term and long-term demographic trends, patterns and trends observed in other countries, government policy, information provided by local planners and other relevant information.

Assumptions for national projections are derived for each single-year of age to produce projections at one-year intervals. The following describes how assumptions are applied for national projections.

Fertility

Projected (live) births are derived by applying age-specific fertility rates to the mean female population of childbearing age. The mean female population for each age is derived by averaging the population at the start and end of each year. The sum of the number of births derived for each age of mother gives the projected number of births for each year.

The female age-specific fertility rates for each year of the projection period represent the number of births to females of each age in each year. The set of age-specific fertility rates for each year is typically summarised by the total fertility rate.

For all population projections, a sex ratio at birth of 105.5 males per 100 females is assumed, based on the historical annual average of the total population.

The fertility assumptions should not be used as a precise measure of fertility or of fertility differentials between groups. It is important to note that the objective of population projections is not to specifically measure or project the fertility of the population. For projection purposes it is more important to have a realistic yet tractable model for projecting fertility trends (and birth numbers) into the future.

Mortality

Mortality assumptions are formulated in terms of survival rates. This is because in the projection model the base population is survived forward each year. The projected number of deaths is calculated indirectly. Survival rates are applied to births and single years of age. There are different survival rates for each age of life and for males and females.

The male and female age-specific survival rates for each year of the projection period represent the proportion of people at each age-sex who will survive for another year. In general, survival rates are highest at ages 5–11 years and then decrease with increasing age. The set of age-sex-specific survival rates for each year is typically summarised by male and female life expectancies at birth.

Annual survival rates are applied separately to the population at the start of each year, births and migrants.

The mortality assumptions should not be used as a precise measure of mortality or of mortality differentials between groups. It is important to note that the objective of population projections is not to specifically measure or project the life expectancy of the population. For projection purposes it is more important to have a realistic yet tractable model for projecting mortality trends (and death numbers) into the future.

Migration

Migration assumptions are formulated in terms of a net migration level and an age-sex net migration pattern for each year of the projection period. Where practical, both the level and age-sex pattern are derived from a detailed analysis of net migration, including:

  • external migration data (from passenger cards):
  • arrivals and departures by country of citizenship
  • New Zealand citizen arrivals and departures by country of source/destination
  • Immigration New Zealand data:
  • residence applications and approvals
  • student and work visas

2020-base to 2073

The 2020-base national population projections (released December 2020) have as a base the estimated resident population (ERP) of New Zealand at 30 June 2020, and cover the period to 2073 at one-year intervals. They superseded by the 2016-base national population projections (released October 2016).

Detailed information on the 2020-base population, assumptions and 'what if' scenarios used can be found here National Population Projections 2020-base

2016-base to 2068

The 2016-base national population projections (released October 2016) have as a base the provisional estimated resident population (ERP) of New Zealand at 30 June 2016, and cover the period to 2068 at one-year intervals. They supersede the 2014-base national population projections (released November 2014).

Detailed information on the base population, assumptions and 'what if' scenarios can be found here: National Population Projections 2016-base

2014-base to 2068

The 2014-base national population projections have been superseded by the 2011-base national population projections (released September 2012).

Detailed information on the 2014 base population, assumptions and 'what if' scenarios used can be found here National Population Projections 2014-base

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