Subnational Family and Household Projections 2013-base

Family and household concepts

These projections are based on the definitions of family and household used in the 2013 Census of Population and Dwellings. A family is defined as a couple, with or without child(ren), or one parent with child(ren), usually living together in a household. It excludes related people, such as siblings, who are not in a couple or parent-child relationship. A household is defined as 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. 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 (ERP) of New Zealand at 30 June 2013. We derived this population (4.442 million) from the census usually resident population count at 5 March 2013 (4.242 million), with adjustments for:

• net census undercount (+104,000)
• residents temporarily overseas on census night (+82,000)
• births, deaths, and net migration between census night and 30 June 2013 (+9,000)
• reconciliation with demographic estimates at ages 0–9 years (+5,000).

For more information about the base population, refer to Population Estimates.

We derived the estimated number of families and households indirectly from the estimated resident population and the estimated living arrangement type rates for each age-sex group. The estimated number of families (1.247 million) and households (1.648 million) are equivalent to the census family count (1.136 million) and census household count (1.550 million), respectively, at 5 March 2013, with adjustments for:

• net census undercount
• families and households temporarily overseas on census night
• change between census night (5 March 2013) and 30 June 2013
• families and households temporarily absent from their usual residence but elsewhere in New Zealand on census night.

Fertility

The assumed fertility rates are based on registered births for each area during the period 2009–13, with change between 2013 and 2038 consistent with the fertility assumptions from the National Population Projections: 2014(base)–2068.

Under the medium fertility assumption, the period total fertility rate at the national level is assumed to decline gradually from 1.95 births per woman in 2015 to 1.92 in 2023 and 1.90 from 2030. In 2014–18 the medium fertility assumption ranges from 1.38 births per woman for Wellington city to 2.90 for Opotiki district. In 2034–38 the assumed total fertility rates range from 1.34 births per woman for Wellington city (low fertility assumption) to 3.01 births per woman for Opotiki district (high fertility 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 are based on registered deaths for each area during the period 2009–13, with change between 2013 and 2038 consistent with the mortality assumptions from the National Population Projections: 2014(base)–2068.

Under the medium mortality assumption, period life expectancy at birth at the national level is assumed to increase from 80.2 years for males and 83.9 years for females in 2015, to 85.5 years for males and 88.7 years for females in 2043. In 2014–18 the medium mortality assumption ranges from 79.7 years for males and 79.5 years for females for Kawerau district, to 84.8 years for males and 88.4 years for females for Queenstown-Lakes district. In 2034–38 the assumed life expectancy at birth ranges from 78.3 years for males and 82.0 years for females for Kawerau district (high mortality assumption), to 89.8 years for males and 92.8 years for females for Queenstown-Lakes district (low mortality 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 intercensal period from 1981 to 2013, 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 149,300 in 2014–18, and 60,000 in each subsequent five-year period. Of the 67 territorial authorities, only 14 are assumed to have the same net migration level in each five-year period between 2013 and 2038. The remaining areas are assumed to have different net migration levels during at least one of the five-year periods. Different 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 some 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.

The age-sex patterns of net migration for each area are based on observed intercensal net migration patterns during 1981–2013, subnational population estimates since 2013, and the latest migration assumptions from the National Population Projections: 2014(base)–2068.

Living arrangement type rates (LATRs)

One LATR variant is used for all three subnational family and household projections. This assumes that LATRs will change linearly between 2013 and 2038, based on an assessment of observed trends between 1986 and 2013 and likely future trends, by sex and 5-year age group. The LATRs are constrained so that the medium projection of the Subnational Family and Household Projections sums to the medium projection 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 LATRs do vary by area, they are generally consistent with assumed trends of LATR variant B at the national level. The main changes in LATRs assumed at the national level between 2013 and 2038 for this variant are:

• Partner in couple-without-children family: Increasing rates for males aged over 70 years. Increasing rates for females aged up to 42 years, and 63 years and older. This reflects lower fertility rates with fewer couples having children, couples having children at older ages, 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: Increasing rates for females at most ages, especially at ages 30–70 years. This reflects lower fertility rates with fewer couples having children and delayed childbearing.
• Child in two-parent family: Increasing rates at most ages, especially at ages 0–30 years. This reflects decreased rates of single parenting from separation, divorce, and childbearing outside couple relationships, as well as children living with parents at older ages.
• Parent in one-parent family: Increasing rates for males. Decreasing rates for females, which reflects decreased rates of single parenting and lower fertility rates.
• Child in one-parent family: Decreasing rates at younger ages, especially at ages 0–20 years. This reflects increased rates of re-partnering of parent.
• Person in other multi-person household: Decreasing rates at most ages. This reflects increasing rates of partnerships.
• Person in one-person household: Increasing rates especially at ages 30–70 years for males. The proportion of females years living alone is assumed to drop, given a slight convergence of male life expectancy to female life expectancy.
• Person in non-private dwelling: Decreasing rates at older ages, associated with increasing life expectancy and well-being and declines in morbidity rates, enabling people to live independently at home longer.
• Average number of families per family household is assumed to increase from 1.050 to 1.075, reflecting increasing co-residence of multi-generational families.
• Average number of people per other multi-person household is assumed to increase from 2.637 to 2.773, reflecting group-living in response to housing costs.
• Proportion of two-parent families with dependent children is assumed to remain constant at 0.817.
• Proportion of one-parent families with dependent children is assumed to remain constant at 0.720.

Regional projections

Family and household projections for regional council areas (regions) are calculated by combining projections for territorial authority (TAs) and Auckland local board (ALBs) areas, or parts of TAs when a TA is split between regions. Of the 67 TAs, 6 TAs are split over two or more regions, while the remaining 61 TAs are completely within one region.

LATRs are calculated at TA and ALB level. For TAs which are split between regions, LATRs for that TA are applied to population projections for each part of the TA.

Those variables which cannot be obtained by summation, such as average family size and average household size, are recalculated for regions after combining the TA and ALB projections.

Alternative series

We have produced six alternative projections by combining three population projections with two variants of living arrangement type rates.

The three population projections are:

• Low which assumes low fertility, high mortality, and low migration
• Medium which assumes medium fertility, medium mortality, and medium migration
• High which assumes high fertility, low mortality, and high migration.

The two living arrangement type rates are:

• A which assumes LATRs will remain constant at 2013 levels B which assumes LATRs will change linearly between 2013 and 2038.

Each family and household projection series is denoted by the population projection and variant of living arrangement type rates. For example, series Medium B denotes that variant 'B' living arrangement type rates have been applied to the medium population projection.

At the time of release, we consider the Medium B projection the most suitable for assessing future family and household changes. Moreover, only Medium B has been formulated to produce demographically plausible results, by assessing both observed trends between 1986 and 2013 and likely future trends to 2038. Other projections 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 A variants are formulated solely from observed historical rates.

The other projections 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, Low B, Medium B, and High B can be used for assessing the effect of different population outcomes combined with variant B living arrangement type rates; and series Medium A and Medium B illustrate the effect of different living arrangement type assumptions combined with the mid-range population scenario.