National Family and Household Projections 2018 base

Reference period This release contains 2018-base projections of families and households usually living in New Zealand. These supersede the 2013-base projections updated released in October 2017. The new projections have the estimated families and households at 30 June 2018 as a base, and cover the period 2023–2043 at five-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. See NZ.Stat for more detailed projection results. Overview of changes to the 2018-base projections The 2018-base projections are derived based on a new method: 'sequential propensity' method and a modelled approach to output future estimates of living arrangement type propensities based on 2001–2018 Census data. This replaces the 'propensity' method used in 2001-base, 2006-base, and 2013-base projections. The family and household projections are derived from estimates (for 2018) and projections (for 2023–2043) 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). The content of the published outputs for these 2018-base projections is consistent with the 2013-base releases of national and subnational family and household projections (National family and household projections: 2013(base)–2038 update, Subnational family and household projections: 2013(base)–2038). However, methods used for structuring the historic living-arrangement-type data and for estimating the living-arrangement-type propensities at future time intervals are different to those used previously. Previous publications of family and household projections have been based on linear interpolation methods for determining plausible scenarios of future living-arrangement propensities given the historic trends observed by the census data. Propensities have been estimated for the output categories only and have not been informed by the distributions of the higher levels of living-arrangement categories and processes were executed separately for national and subnational projections. A key advantage of this new method is it allows for the simultaneous production of national and subnational projections, and provides scope for future enhancements. The changes to the 2018-base publication of family and household projections are summarised as: national and subnational projections of population by living-arrangement type, families by family type, and households by household type are published simultaneously both national and subnational projections of population by living-arrangement type, families by family type, and households by household type are produced for five-yearly intervals at 30 June 2018–2043 (previously, national projections were available at yearly intervals) national projections and regional council projections are produced by aggregating the projections for territorial authorities, including the areas split across regions living-arrangement-type categories have been derived based on consistent use of the 2001 to 2018 Censuses family coding and household composition information structuring the historic counts of living-arrangement-type information sequentially into progressively more detailed categories has potentially improved the quality of the estimated propensities used to produce the projections of population by living-arrangement type, and of families and households the modelled approach provides opportunities for future enhancements, such as incorporating uncertainty estimates of the living-arrangement-type propensities into the variants of the projections, and outputting projections of subpopulations by living-arrangement type. See 2018-base family and household projections: Data and methods for detailed data and methods used to produce the 2018-base family and household projections. Projection assumptions We formulated the projection assumptions after analysing short-term and long-term historical trends, recent trends and patterns observed in other countries, government policy, and other relevant information. Base population The estimated resident population at 30 June 2018 forms the base population for deriving postcensal population estimates. We derived the estimated resident population of New Zealand at 30 June 2018 (4,900,600) from the 2018 Census usually resident population count at 6 March 2018 (4,799,655), with adjustments for: residents missed or counted more than once by the census (net census undercount) (+124,900) residents temporarily overseas on census night (+77,200) natural increase (births less deaths) between census night and 30 June 2018 (+8,000) net migration between census night and 30 June 2018 (+7,300) reconciliation with demographic estimates at ages 0–14 years (-16,600). See National population estimates (2018-base) for more details. 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 (1.38 million) and households (1.79 million) are equivalent to the census family count (1.21 million) and census household count (1.65 million), respectively, at 6 March 2018, with adjustments for: net census undercount families and households temporarily overseas on census night change between census night (6 March 2018) and 30 June 2018 families and households temporarily absent from their usual residence but elsewhere in New Zealand on census night. Which projection should I use? 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 2018 levels B modelled LATRs based on 2001-2018 census results. 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 2001 and 2018 and likely future trends to 2043. 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. Consistency with other projections These family and household projections complement National Population Projections: 2020(base)–2073 released on 08 December 2020. However, only the medium projection of the family and household projections and the median projection (50th percentile) of the national population projections are designed to be directly comparable. Other projections or percentiles cannot be directly compared because the projection assumptions may be incompatible. en-NZ