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National Family and Household Projections: 2006 (base) - 2031
Embargoed until 10:45am  –  08 December 2008
Technical notes

Latest projections

This release contains the 2006-base projections of families and households usually living in New Zealand. The family and household projections have been produced using the 2006-base national population projections released on 24 October 2007. The projections cover the period 2007–31 at one-year intervals. The projection period is limited to 25 years because of the uncertainty of family and household projections, as discussed in 'Nature of projections' (below).

As with both sets of 2001-base national family and household projections (released in June 2003 and June 2005), a 'propensity' method has been used to produce the latest projections. The family and household projections are derived from projections (for 2007–31) of the New Zealand population, by multiplying the population by 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). Before the 2001-base projections, household projections were produced using a 'household head' method.

Family and household concepts

These projections are based on the definitions of family and household used in the 2006 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 (for example, eating facilities, cooking facilities, bathroom and toilet facilities, a living area) in a private dwelling. No information is available from the census on families and households extending beyond a single dwelling, or on families defined using different concepts (for example, 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). No information is 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 New Zealand at 30 June 2006. This population (4.185 million) was based on the census usually resident population count (4.028 million) at 7 March 2006 with adjustments for:

  1. net census undercount (+80,000)
  2. residents temporarily overseas on census night (+64,000)
  3. births, deaths and net migration between census night (7 March 2006) and 30 June 2006 (+9,000)
  4. reconciliation with demographic estimates at ages 0–9 years (+3,000).

The estimated numbers of families and households are derived indirectly from the estimated resident population and the estimated living arrangement type rates for each age-sex group. The estimated number of families (1.168 million) and households (1.553 million) are equivalent to the census family count (1.068 million) and census household count (1.454 million), respectively, at 7 March 2006, with adjustments for:

  1. net census undercount
  2. families and households temporarily overseas on census night
  3. change between census night (7 March 2006) and 30 June 2006
  4. families and households temporarily absent within New Zealand.

For more information about the base population, refer to Information about the population estimates on the Statistics New Zealand website: www.stats.govt.nz.

Alternative series

Six alternative series have been produced by combining three population projection series with three variants of living arrangement type rates. The three population projection series are:

  • series 1 which assumes low fertility, high mortality and low migration
  • series 5 which assumes medium fertility, medium mortality and medium migration
  • series 9 which assumes high fertility, low mortality and high migration.

At the time of release, projection series 5B is considered the most suitable for assessing future family and household changes. Moreover, only series 5B has been formulated to produce demographically plausible results by assessing both observed trends between 1986 and 2006, and likely future trends to 2031. Other series may project significantly different numbers of male and female partners in 'couple without children' and/or 'two-parent' families, because the living arrangement type rate variants A are formulated solely from observed historical rates.

The other projection series allow users to assess the impact on the number of families and households resulting from different population and/or living arrangement type scenarios. For example, series 1B, 5B and 9B can be used for assessing the effect of different population outcomes combined with variant B living arrangement type rates; and series 5A and 5B illustrate the effect of different living arrangement type assumptions combined with the mid-range population scenario.

More detailed projection results, including projections for individual years, are available on request. Special projections can also be produced for clients using their own assumptions. For more information and quotes, email demography@stats.govt.nz.

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 multi-person households = number of people in other multi-person households ÷ average number of people per other multi-person household.

Projection assumptions

Projection assumptions are formulated after analysis of short-term and long-term historical trends, recent trends and patterns observed in other countries, government policy, and other relevant information.

Fertility

There are three alternative fertility variants – designated low, medium and high – which assume that fertility rates will vary until the year 2026 when the total fertility rate will reach 1.70, 1.90 and 2.10 births per woman, respectively. After 2026, fertility rates are assumed to stay constant. The base total fertility rate in 2006 was 1.99 births per woman (based on estimated births by date of occurrence).

The medium fertility variant assumes fertility rates of women aged under 32 years will decline between 2006 and 2026, while rates for women aged 32 years and over will increase. By comparison, the low fertility variant assumes fertility rates will decrease between 2006 and 2026 for most ages. The high fertility variant assumes that fertility rates will drop between 2006 and 2026 for women aged under 31 years and increase for women aged 31 years and over.

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

 Graph, Total Fertility Rate.

Mortality

There are three alternative mortality variants – designated low, medium and high – which assume that mortality rates will continue to drop so that life expectancy at birth will increase to 84.3, 82.5 and 80.8 years for males, respectively, by 2031. The corresponding life expectancies for females in 2031 will be 87.6, 86.2 and 84.8 years. The base life expectancy at birth in 2005–07 was 78.2 years for males and 82.2 years for females.

Mortality rates are assumed to decrease at the same rate at all ages. Between 2006 and 2031, male mortality rates are assumed to decrease by about 42, 32 and 21 percent for the low, medium and high mortality variants, respectively. By comparison, female mortality rates are assumed to decrease by about 41, 32 and 22 percent for the low, medium and high mortality variants, respectively.

 Graph, Life Expectancy at Birth.

Migration

There are three alternative migration variants – designated low, medium and high – which assume long-run annual net migration levels of 5,000, 10,000 and 15,000, respectively. Short-run migration levels converging to the long-run levels are assumed for 2007–09. These short-run levels are based on an analysis of immigration permits, residence applications and approvals, overseas student numbers, and arrivals and departures analysed by characteristics such as citizenship, country of last/next permanent residence and age.

 Graph, Net Migration.

Consistent with historical and recent trends, the age-sex patterns of net migration assume the main net outflow at ages 21–25 years, mainly due to young New Zealanders embarking on international travel and the departure of overseas students after completing their study in New Zealand. Net inflows are assumed for most other ages, with the highest net inflows at 15–19 and 27–38 years.

Living arrangement type rates (LATRs)

There are two alternative LATR variants – designated A and B. Variant A assumes that LATRs will remain constant at 2006 levels. Variant B assumes that LATRs will change linearly between 2006 and 2031 based on an assessment of observed trends between 1986 and 2006, and likely future trends, by sex and single-year of age.  

Variant B is the preferred variant, because it has been formulated to produce demographically plausible results. For variant B, the main changes in LATRs assumed between 2006 and 2031 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 25–54 and 70–84 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 25–59 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 30–45 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 multi-person household: Increasing rates at most ages, especially 15–24 years associated with higher numbers of students.
  7. Person in one-person household: Increasing rates at most ages, especially 30–89 years for males and 35–54 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.

For variants A and B, the following factors remain constant at the 2006 levels:

  • the average number of families per family household is assumed to remain constant at 1.041 from 2006–31
  • the average number of people per other multi-person household is assumed to remain constant at 2.600 from 2006–31
  • the proportion of two-parent families with dependent children is assumed to remain constant at 0.832 from 2006–31
  • the proportion of one-parent families with dependent children is assumed to remain constant at 0.754 from 2006–31.

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 projections are based on assumptions made about future fertility, mortality, net 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.

The projections do not take into account non-demographic factors (for example, 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.

Only series 5B has been formulated to produce demographically plausible results by assessing both observed historical trends and likely future trends. Other series may project significantly different numbers of male and female partners in 'couple without children' and/or 'two-parent' families, because the living arrangement type rate variants 'A' are formulated solely from observed historical rates.

Although living arrangement type rate variant 'B' is formulated to account for changing social patterns, there is uncertainty about how different social patterns will inter-relate 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 re-partnering, and dissolution
  • propensity of young adults to stay in the parental home
  • propensity and ability of people to live alone
  • presence of other relatives (for example, extended family) and non-related individuals (for example, 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 Information about the demographic projections 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 divided 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 dependent child is a child in a family who is aged under 18 years and not in full-time employment (regularly working for 30 hours or more per week).

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 New Zealand is an estimate of all people who usually live in New Zealand at a given date. It includes all residents 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 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 multi-person 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:

  • Partner in couple without children family: A person usually living in a partner role, but not in a parent role.
  • 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.
  • Partner/parent in two-parent family: A person usually living in a partner and parent role.
  • Child in two-parent family: A person usually living in a child role with two parents, but not in a partner or parent role.
  • Other person with two-parent family: A person usually living with a two-parent family, but not in a partner, parent or child role.
  • Parent in one-parent family: A person usually living in a parent role, but not in a partner role.
  • Child in one-parent family: A person usually living in a child role with one parent, but not in a partner or parent role.
  • Other person with one-parent family: A person usually living with a one-parent family, but not in a partner, parent or child role.
  • Person in other multi-person household: A person usually living with one or more people not in partner, parent or child roles.
  • Person in one-person household: A person usually living alone.
  • 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.

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 NZ must be acknowledged as the source.

Liability

While care has been used in processing, analysing and extracting information, Statistics NZ gives no warranty that the information supplied is free from error. Statistics NZ 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 NZ. Statistics NZ accepts no responsibility for any such delays.

For information on the changing face of older New Zealanders, visit www.stats.govt.nz/older-people

 

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