Latest projections
This release contains the 2001-base projections of families and households usually living in New Zealand. A 'propensity' method has been used to produce the latest projections, superseding the 1996-base household projections (released in March 1998) which used a 'household head' method. The new series include, for the first time, projections of families by broad family type and projections of broad household types. Projections of the population by living arrangement type, sex and single year of age (to 90+ years) are also available.
The projections cover the period 2002–2021 at one-year intervals. The projection period is limited to 20 years because of the uncertainty of family and household projections as discussed in Nature of projections (below).
The family and household projections are derived from the complementary projections of the New Zealand population (National Population Projections released on 24 October 2002) by multiplying the projected 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).
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 consists of two or more people usually living together as a couple and/or in a parent-child relationship 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 on families and households extending beyond a single dwelling, nor on families and households 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 coterminous. 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. In theory, parents and children can be of any age. In addition, 'other people' living with families include both 'related' (eg siblings) and 'non-related' (eg boarders) people who are not themselves in a couple and/or parent-child relationship in that household.
Base population
The population projections have as a base the estimated resident population of New Zealand at 30 June 2001. This population (3.880 million) was based on the census usually resident population count (3.737 million) at 6 March 2001 and adjusted for:
- net census undercount (+81,000)
- residents temporarily overseas on census night (+55,000)
- births, deaths and net migration between census night (6 March 2001) and 30 June 2001 (+4,000)
- reconciliation with demographic estimates at ages 0–9 years (+4,000).
The base number of families and households is derived indirectly from the estimated resident population and the estimated living arrangement type rates for each age-sex group. The estimated number of families (1.052 million) was based on the census family count (968,000) at 6 March 2001 and adjusted for:
- families temporarily absent within New Zealand (+47,000)
- net census undercount (+18,000)
- families temporarily overseas on census night (+13,000)
- change between census night (6 March 2001) and 30 June 2001 (+6,000).
Similarly, the estimated number of households (1.441 million) was based on the census household count (1.344 million) at 6 March 2001 and adjusted for:
- households temporarily absent within New Zealand (+45,000)
- net census undercount (+25,000)
- households temporarily overseas on census night (+17,000)
- change between census night (6 March 2001) and 30 June 2001 (+9,000).
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 "Information about the population estimates" on the Statistics New Zealand website (www.stats.govt.nz).
Alternative series
Nine alternative series have been produced using different combinations of migration and living arrangement type assumptions.
At the time of this release, projection series 4B is considered the most suitable for assessing future family and household changes. Moreover, only series 4B has been formulated to produce demographically plausible results by assessing both observed trends between 1986 and 2001, and likely future trends to 2021. 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 and C 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 combinations of migration and living arrangement type assumptions. Series 3B, 4B and 5B can be used for assessing the effect of the different migration assumptions combined with variant B living arrangement type rates; and series 4A, 4B and 4C allow for different living arrangement type rate assumptions combined with medium migration. In addition, series 3A, 4A and 5A can be used for assessing the effect of the different migration assumptions combined with variant A (no change) living arrangement type rates; series 3C, 4C and 5C can be used for assessing the effect of the different migration assumptions combined with variant C living arrangement type rates.
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 info@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 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, recent trends and patterns observed in other countries, government policy, and other relevant information.
Fertility
The National Population Projections adopted three alternative fertility variants – designated low, medium and high – which assume that fertility rates will vary until the year 2011 when the total fertility rate will reach 1.60, 1.85 and 2.10 births per woman, respectively. After 2011, fertility rates are assumed to stay constant. The estimated base rate in 2001 was 1.97 births per woman.
The medium fertility variant has been used in all nine alternative series of the family and household projections, as the low and high fertility variants make an insignificant difference to the projected number of families and households. The medium fertility variant assumes fertility rates of women aged under 32 years will decline between 2001 and 2011, with rates increasing slightly for women aged 32 years and over. A sex ratio at birth of 105.5 males per 100 females is assumed, based on the historical annual average.
Mortality
The National Population Projections adopted three alternative mortality variants – designated low, medium and high – which assume that mortality rates will continue to drop so that the average life expectancy at birth for males will increase to 81.2, 80.3 and 79.4 years, respectively, by 2021. The corresponding life expectancies for females in 2021 will be 85.5, 84.8 and 84.0 years. The estimated base life expectancies in 2001 were 76.1 years for males and 81.0 years for females.
The medium mortality variant has been used in all nine alternative series of the family and household projections, as the low and high mortality variants make an insignificant difference to the projected number of families and households. Mortality rates are assumed to decrease at the same rate at all ages. Between 2001 and 2021, male and female mortality rates are assumed to decrease by about 31 and 30 percent, respectively, for the medium mortality variant.
Migration
Alternative long-term annual net migration levels of 0, 5,000 and 10,000 have been used in the family and household projections. The 5,000 net migration level represents the annual average over both the last 15 years and last 100 years.
Short-term net migration levels converging to the long-term levels are assumed for 2002–2006, based on recent trends of arrivals and departures of New Zealand citizens and non-New Zealand citizens. Series with long-term annual net migration of 0 assume net migration in 2003 of 27,000 and in 2004 of 5,000. Series with long-term annual net migration of 5,000 assume net migration in 2003 of 35,000, in 2004 of 16,000, in 2005 of 9,000 and in 2006 of 7,000. Series with long-term annual net migration of 10,000 assume net migration in 2003 of 35,000 and in 2004 of 16,000.
Consistent with historical and recent trends, the age-sex patterns of net migration assume a net outflow at ages 21–27 years associated with students returning overseas after studying in New Zealand and young New Zealanders embarking on overseas travel. Net inflows are assumed at most other ages with the highest net inflows at ages 14–19 years and 29–33 years associated with students from overseas and returning New Zealanders, respectively.
Living arrangement type rates (LATRs)
There are three alternative LATR variants – designated A, B and C. Variant A assumes that LATRs will remain constant at 2001 levels. Variant B 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 single-year of age. Variant C assumes that LATRs will change linearly between 2001 and 2021 according to the linear trend observed between 1986 and 2001, by sex and single-year of age.
For variant B, the main changes in LATRs assumed between 2001 and 2021 are:
- 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.
- 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.
- 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.
- Parent in one-parent family: Increasing rates at most ages, especially at ages 25–39 years. This reflects increased rates of single parenting.
- Child in one-parent family: Increasing rates at most ages, especially at ages 0–19 years. This reflects increased rates of single parenting.
- Person in other multiperson household: Increasing rates at ages 15–24 years associated with higher numbers of students.
- 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.
- 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 variant A, the following factors remain constant at the 2001 levels, while for variants B and C:
- 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
- the proportion of two-parent families with dependent children is assumed to increase linearly from 0.835 in 2001 to 0.850 in 2021
- the proportion of one-parent families with dependent children is assumed to increase linearly from 0.77 in 2001 to 0.78 in 2021.
Nature of projections
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 rather than exact forecasts. They provide an indication of the overall trend but do not attempt to project specific annual variation.
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 will be revised to reflect new trends and to maintain their relevance and usefulness.
Only series 4B 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 and C 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 marriage
- fertility rates, timing of childbearing and average family size
- morbidity and mortality rates
- rates of marriage dissolution and remarriage
- 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)
- study, work and shared care arrangements where people are associated with more than one household
- mobility of the population
- affordability of tertiary education and housing
- 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 number of people in families divided by the number of families.
Average household size is the number of people in households divided 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 usually living together in a registered marriage or consensual union. Couples can be opposite-sex or same-sex.
A dependent child is a person 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.
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Couple without children family: A couple without child(ren), with or without other people, usually living together in a household.
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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.
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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.
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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.
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Other multiperson household: A household containing two or more people usually living together, but not in couple or parent-child relationships with each other.
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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 multiperson 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.
A parent is a person of any age usually living with, and providing care for, at least one natural, step, adopted or foster child (not usually living with a partner or child of their own).
A parent-child relationship consists a parent usually living with, and providing care for, at least one natural, step, adopted or foster child.
A partner is a person of any age usually living 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).
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