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Subnational Family and Household Projections: 2001(base) – 2021 update
Embargoed until 10:45am  –  27 October 2005
Technical notes

Latest projections

This release contains 2001-base projections of families and households usually living in the 16 regional council areas and 74 territorial authority areas of New Zealand. The family and household projections have been updated using the 2001-base national family and household projections released on 1 June 2005 and the 2001-base subnational population projections released on 28 February 2005. The projections cover the period 2006–2021 at five-year intervals. The projection period is limited to 20 years because of the uncertainty of these projections, as discussed in the 'Nature of projections' section below.

As with the previous 2001-base subnational family and household projections (released 27 August 2004), a 'propensity' method has been used to produce the latest projections. The family and household projections are derived from estimates (for 2001) and projections (for 2006–2021) of the population for each area, by multiplying the population by the assumed living arrangement type rates for each age-sex group. The projections of population by living arrangement type are subsequently aggregated to give projections of families (by broad family type) and households (by broad household type). Prior to the 2001-base projections, household projections were produced using 'household head' method.

Family and household concepts

These projections are based on the definitions of family and household used in the 2001 Census of Population and Dwellings. A family is defined as a couple, with or without children, or one parent with children, usually living together in a household. A household is defined as one person usually living alone, or two or more people usually living together and sharing facilities (eg eating facilities, cooking facilities, bathroom and toilet facilities, a living area), in a private dwelling. No information is available from the census on families or households extending beyond a single dwelling, or on families defined using different concepts (eg whanau), and minimal information is available on families in non-private dwellings.

In these family and household projections, all people are allocated to one of 11 living arrangement types. The living arrangement type refers to the usual family and household role of a person, based on a combination of individual, family, household and dwelling information from the census. The projections are based on allocating people to one role from several broad roles they may have within each social structure. These roles vary by age and sex and are assumed to change over time with changes in social patterns.

The projections do not give a complete picture of the complexity of family and household structures, because people can and do have more than one living arrangement type role in any one entity, and families and households are not necessarily synonymous. Although people can have more than one residence, their living arrangement type role is generally based on the family and household structure of where they usually live, as self-identified by them in the census. Because households are defined as discrete units, the fluidity of living arrangements where people are associated with more than one household for study, work or shared-care purposes is not addressed.

Opposite-sex and same-sex couples are not projected separately, but are included in projections of 'couple without children' and 'two-parent' families.

It is also important to note that the definitions of parents and children are social, not biological. For example, parents include people aged 15 years or over usually living with at least one of their natural, step-, adopted or foster children (who is not usually living with a partner or child of their own). Similarly, a child is a person of any age usually living with one or two natural, step- or adopted parents (but not usually living with a partner or child of their own). There is no information available on the strength of identified parent-child relationships in terms of emotional and/or financial support.

Base population

These projections have as a base the estimated resident population of each area at 30 June 2001.This population was based on the census usually resident population count of each area at 6 March 2001 with adjustments for:

  • net census undercount
  • residents temporarily overseas on census night
  • births, deaths and net migration between census night (6 March 2001) and 30 June 2001
  • reconciliation with demographic estimates at ages 0–9 years.

The estimated numbers of families and households at 30 June 2001 were derived indirectly from the estimated resident population and the estimated living arrangement type rates for each age-sex group. The estimated numbers of families and households of each area are equivalent to the census family count and census household count, respectively, at 6 March 2001 with adjustments for:

  • net census undercount
  • families and households temporarily overseas on census night
  • change between census night and 30 June 2001
  • families and households temporarily away from their usual residence, but in New Zealand, on census night.

The estimated and projected population, families and households are not directly comparable with census counts because of these adjustments. For more information about the base population, refer to the 'Information about the population estimates' page on the Statistics New Zealand website (www.stats.govt.nz).

Alternative series

Three alternative subnational family and household projection series (designated low, medium and high) have been produced for each area using different population projection series (with different fertility, mortality and migration assumptions). One set of living arrangement type assumptions has been used for all three series.

At the time of release, the medium projection series is considered the most suitable for assessing future family and household changes. The medium projection series is derived from the medium series of the 2001-base Subnational Population Projections (released 28 February 2005), which assumes medium fertility, medium mortality and medium net migration for each area. The medium subnational family and household projection series is also consistent with series 5B of the 2001-base National Family and Household Projections (released 1 June 2005) and series 5 of the 2004-base National Population Projections (released 16 December 2004).

The low and high projection series allow users to assess the impact on the number and type of families and households resulting from different population scenarios. The low and high series have been formulated to give plausible alternative scenarios for each area rather than at any collective geographical level. Neither series is consistent with the low and high series of the 2001-base Subnational Population Projections or any of the alternative series of the 2001-base National Family and Household Projections. The low projection series uses low fertility, high mortality and low net migration for each area. The high projection series uses high fertility, low mortality and high net migration for each area.

More detailed projection results are available on the Statistics New Zealand website (www.stats.govt.nz/people/population/populationprojections.htm) or on request. Special projections can also be produced for clients using their own assumptions. For more information and quotes, email demography@stats.govt.nz. or phone toll-free 0508 525 525.

Method

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

The propensity method has subsequently been used to derive the family and household projections. In this method, living arrangement type rates (or propensities) are applied to population projections to give projections of the population in different living arrangement types. These projections are subsequently aggregated to give projections of families (by broad family type) and households (by broad household type).

The number of couple without children families = (male partners in couple without children families + female partners in couple without children families) ÷ 2.

The number of two-parent families = (male partners/parents in two-parent families + female partners/parents in two-parent families) ÷ 2.

The number of one-parent families = male parents in one-parent families + female parents in one-parent families.

The number of family households = number of families ÷ average number of families per family household.

The number of one-person households = number of people in one-person households.

The number of other multiperson households = number of people in other multiperson households ÷ average number of people per other multiperson household.

Projection assumptions

Projection assumptions are formulated after analysis of short- and long-term historical trends, government policy, information provided by local planners and other relevant information. Tables containing the fertility, mortality and migration assumptions for each territorial authority and regional council area are available in the subnational population projections section of the 'Information about the demographic projections' page on the Statistics New Zealand website (www.stats.govt.nz).

Fertility

The assumed fertility rates are based on the registered births for each area during the period 2002–2004 and change consistent with the medium fertility variant of the National Population Projections.

Under the medium fertility assumption, the total fertility rate at the national level is assumed to increase from 1.97 births per woman in 2001 to 2.01 in 2004–2005, decrease to 1.85 in 2016, and then remain constant. The assumed total fertility rate in 2002–2006 ranges from 3.04 births per woman for Kawerau District to 1.20 for Queenstown-Lakes District.

The high and low fertility assumptions for each area are for a total fertility rate for each five-year period ±0.1 births per woman from the medium assumption.

A sex ratio at birth of 105.5 males per 100 females is assumed, based on the historical annual average at the national level.

Mortality

The assumed mortality rates for each area are based on the registered deaths for each area during the period 2002–2004 and change consistent with the medium mortality variant of the National Population Projections.

Under the medium mortality assumption, life expectancy at birth at the national level is assumed to increase from 76.1 years for males and 81.0 years for females in 2001, to 80.7 years for males and 84.8 years for females in 2021. The assumed life expectancy at birth in 2002–2006 ranges from 72.2 years for males and 77.2 years for females for Wairoa District to 81.5 years for males and 85.7 years for females for Queenstown-Lakes District.

The low and high mortality assumptions for each area are for a life expectancy at birth for each five-year period ±0.5 years from the medium assumption.

Migration

Migration at the subnational level has both an internal (to/from other areas of New Zealand) and an external (to/from overseas) component, although these separate components are difficult to quantify. The assumed net migration for each area is based on a consideration of observed net migration during each five-year period from 1981 to 2001, the capacity of the area for further growth (for areas with net inflow), whether historical outflows can be sustained (for areas with net outflow), the desirability of the area to new migrants, and information available from and about local authorities relating to current and future developments which may affect population change.

Under the medium migration assumption, net migration at the national level is assumed to be 104,000 in 2002–2006, 38,000 in 2007–2011 and 50,000 in each subsequent five-year period. Of the 74 territorial authority areas, 16 are assumed to have the same net migration level in each five-year period between 2001 and 2021. The remaining areas are assumed to have differing net migration levels during at least one of the five-year periods. Differing levels are generally assumed for areas susceptible to changes in external migration, such as university cities (which have attracted large numbers of overseas students in recent years), and areas where constant net outflows are considered unsustainable.

The low and high net migration assumptions are chosen to represent plausible alternative migration scenarios for each area rather than at the collective national level. The age-sex patterns of net migration for each area are based on observed intercensal net migration patterns during 1981–2001.

Living arrangement type rates (LATRs)

One LATR variant is used for all three subnational family and household projection series. This assumes that LATRs will change linearly between 2001 and 2021, based on an assessment of observed trends between 1986 and 2001, and likely future trends, by sex and five-year age group. The LATRs are constrained so that the medium series of the Subnational Family and Household Projections sums to series 5B of the National Family and Household Projections for population (by living arrangement type, five-year age group and sex), for families (by family type) and for households (by household type).

While assumed trends in living arrangement type rates do vary by area, they are generally consistent with assumed trends of LATR variant B at the national level. The main changes assumed at the national level between 2001 and 2021 for this variant are:

  1. Partner in couple without children family: Increasing rates for males and females at most ages, especially at ages 30–54 years for males, and 30–44 and 85–94 years for females. This reflects lower fertility rates, with fewer couples having children, and a slight convergence of male life expectancy to female life expectancy, with more couples having both partners living to older ages.
  2. Partner/parent in two-parent family: Decreasing rates for males and females at most ages, especially at ages 25–64 years for males and 25–54 years for females. This reflects lower fertility rates, with fewer couples having children.
  3. Child in two-parent family: Decreasing rates at most ages, especially at ages 0–19 years. This reflects increased rates of single parenting from separation, divorce, childbearing outside of couple relationships, and more complex shared-care arrangements.
  4. Parent in one-parent family: Increasing rates at most ages, especially at ages 25–39 years. This reflects increased rates of\single parenting.
  5. Child in one-parent family: Increasing rates at most ages, especially at ages 0–19 years. This reflects increased rates of single parenting.
  6. Person in other multiperson household: Increasing rates at ages 15–24 years associated with higher numbers of students.
  7. Person in one-person household: Increasing rates at most ages, especially 30–74 years for males and 35–44 years for females. These increases are associated with increased rates of marriage dissolution, decreasing rates of people forming partnerships, and lower fertility rates. The proportion of females aged 60–79 years living alone is assumed to drop slightly, given a slight convergence of male life expectancy to female life expectancy.
  8. Person in non-private dwelling: Increasing rates at ages 15–24 years associated with higher numbers of students. Decreasing rates at ages 85+ years associated with increasing life expectancy and declines in morbidity rates.

Additionally, assumptions of the average number of families per family household were formulated from historical trends, and the average number of people per other multiperson household was assumed to increase at an equal rate for all areas. At the national level:

  • the average number of families per family household is assumed to increase linearly from 1.032 in 2001 to 1.040 in 2021
  • the average number of people per other multiperson household is assumed to increase linearly from 2.65 in 2001 to 2.90 in 2021.

Nature of projections

Demographic 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 family and household projections are based on assumptions made about future fertility, mortality, migration and living arrangement type patterns of the population. Although the assumptions are carefully formulated to represent future trends, they are subject to uncertainty. Therefore, the projections should be used as guidelines and an indication of the overall trend, rather than as exact forecasts.

Demographic projections should not be confused with economic forecasts. Changes in the number of people, families or households do not necessarily relate to the social and economic well-being of an area. The number of people, families and households may change independent of local economic factors.

Household numbers should not be confused with building activity or dwelling numbers. Households refer to private dwellings that are usually occupied by a person or group of people. Households therefore exclude non-private dwellings, unoccupied dwellings and dwellings which are not the usual residence of people (eg holiday homes, second homes).

The projections do not take into account non-demographic factors (eg war, catastrophes, major government and business decisions) which may invalidate the projections. Demographic trends are monitored regularly and, when it is necessary, the projections are revised to reflect new trends and to maintain their relevance and usefulness.

Although the living arrangement type rates are formulated to account for changing social patterns, there is uncertainty about how different social patterns will interrelate and vary by age-sex and/or birth cohort. Relevant social patterns include changes in:

  • age of cohabitation and/or marriage
  • fertility rates, timing of childbearing and average family size
  • morbidity and mortality rates
  • rates of partnership formation, including repartnering, and dissolution
  • propensity of young adults to stay in the parental home
  • propensity and ability of people to live alone
  • presence of other relatives (eg extended family) and non-related individuals (eg boarders) in a household
  • study, work and shared-care arrangements where people are associated with more than one household
  • geographic location and mobility of the population
  • external migration patterns, including students from overseas
  • affordability of tertiary education, housing and healthcare
  • ethnic mix of the New Zealand population.

For more information about the projections, refer to the 'Information about the demographic projections' page on the Statistics New Zealand website (www.stats.govt.nz.).

Definitions

Average family size is the mean number of people per family. It is calculated by dividing the number of people in families by the number of families.

Average household size is the mean number of people per household. It is calculated by dividing the number of people in households by the number of households.

A child is a person of any age usually living with one or two natural, step- or adopted parents, but not usually living with a partner or child of their own.

A couple consists of two people aged 15 years and over usually living together in a registered marriage or consensual union. Couples can be opposite-sex or same-sex.

A dwelling is a structure, part of a structure, or group of structures that is used, or intended to be used, as a place where people reside.

  • A non-private dwelling provides short- or long-term communal or transitory type accommodation. Non-private dwellings are generally available to the public by virtue of employment, study, special need, legal requirement or recreation. They include institutions and group-living quarters such as hotels, motels, hospitals, retirement homes, prisons, hostels, motor camps, boarding houses, defence barracks, ships and trains.
  • A private dwelling accommodates a person or group of people and is generally unavailable for public use. The main purpose of a private dwelling is as a place of habitation for residents who usually live independently within the community.

The estimated resident population of each area is an estimate of all people who usually live in that area at a given date. This estimate includes all residents of that area present in New Zealand and counted by the census (census usually resident population count), residents who are temporarily overseas (who are not included in the census), and an adjustment for residents missed or counted more than once by the census (net census undercount). Visitors from elsewhere in New Zealand or from overseas are excluded.

A family consists of a couple, with or without child(ren), or one parent with child(ren), usually living together in a household. Related people, such as siblings, who are not in a couple or parent-child relationship, are therefore excluded from this definition.

  • Couple without children family: A couple without child(ren), with or without other people, usually living together in a household.
  • Two-parent family:  A couple with child(ren), with or without other people, usually living together in a household. Any children are not usually living with a partner or child of their own.
  • One-parent family:  One parent with child(ren), with or without other people, usually living together in a household. Any children are not usually living with a partner or child of their own.

A household consists of either one person usually living alone, or two or more people usually living together and sharing facilities (eg eating facilities, cooking facilities, bathroom and toilet facilities, a living area), in a private dwelling.

  • Family household: A household containing two or more people usually living together with at least one couple and/or parent-child relationship, with or without other people.
  • Other multiperson household: A household containing two or more people usually living together, but not in couple or parent-child relationships with each other.
  • One-person household: A household containing one person usually living alone.

Life expectancy is the average length of life remaining at a given age. As derived from a period life table, it assumes that a person experiences the age-specific mortality rates of a given period from the given age onwards. It represents the average longevity of the whole population and does not necessarily reflect the longevity of an individual.

Living arrangement type is the usual family and household role of a person based on a combination of individual, family, household and dwelling information. As used in these family and household projections, all people are allocated to one of 11 living arrangement types:

  1. Partner in couple without children family: A person usually living in a partner role, but not in a parent role.
  2. Other person with couple without children family: A person usually living with a couple without children family, but not in a partner, parent or child role.
  3. Partner/parent in two-parent family: A person usually living in a partner and parent role.
  4. Child in two-parent family: A person usually living in a child role with two parents, but not in a partner or parent role.
  5. Other person with two-parent family: A person usually living with a two-parent family, but not in a partner, parent or child role.
  6. Parent in one-parent family: A person usually living in a parent role, but not in a partner role.
  7. Child in one-parent family: A person usually living in a child role with one parent, but not in a partner or parent role.
  8. Other person with one-parent family: A person usually living with a one-parent family, but not in a partner, parent or child role.
  9. Person in other multiperson household: A person usually living with one or more people not in partner, parent or child roles.
  10. Person in one-person household: A person usually living alone.
  11. Person in non-private dwelling: A person usually living in a non-private dwelling.

A living arrangement type rate is the proportion of the population in a living arrangement type, usually disaggregated by age and sex.

A parent is a person of any age usually living with at least one of their natural, step, adopted or foster children (not usually living with a partner or child of their own).

A parent-child relationship consists of a parent usually living with, and providing care for, at least one natural, step-, adopted or foster child.

A partner is a person aged 15 years and over usually living with another person aged 15 years and over in a registered marriage or consensual union.

Regional council areas (regions) were established in 1989. There are 16 regions, covering every territorial authority in New Zealand with the exception of Chatham Islands Territory. There are eight instances where territorial authority boundaries straddle regional boundaries.

The resident population concept is a statistical basis for a population in terms of those who usually live in a given area at a given time. The census usually resident population count is a census measure of the resident population concept, and the estimated resident population is a demographic measure of the resident population concept. In terms of vital statistics, the resident population concept refers to events that relate to residents of New Zealand only.

Territorial authority areas were established in 1989 and are the smallest local government entities. There are 74 territorial authorities, comprising 16 cities, 57 districts and one territory.

The total fertility rate is the average number of live births that a woman would have during her life if she experienced the age-specific fertility rates of a given period (usually a year).

Copyright

Information obtained from Statistics New Zealand may be freely used, reproduced, or quoted unless otherwise specified. In all cases Statistics New Zealand must be acknowledged as the source.

Liability

While care has been used in processing, analysing and extracting information, Statistics New Zealand gives no warranty that the information supplied is free from error. Statistics New Zealand shall not be liable for any loss suffered through the use, directly or indirectly, of any information, product or service.

Timing

Timed statistical releases are delivered using postal and electronic services provided by third parties. Delivery of these releases may be delayed by circumstances outside the control of Statistics New Zealand. Statistics New Zealand accepts no responsibility for any such delays.

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