Household projections: notes and definitions for data analysts
Methodology for calculating long-term household projections, with notes and definitions for household estimates and analysis of data quality.
This guidance is to be read in conjunction with the series on household projections, which includes the latest statistical releases on household projections.
The current methodology in England reflects work to improve the household projections outputs and methods to better meet user needs. This work culminated in a technical consultation about proposed changes to the national statistics on household projections in March 2010.
The background research to this methodology consultation can be found in Testing methodological changes to the household projections model: research report (published 1 March 2010), which is a report to test the impacts of changes to the household projections methods as proposed in the Options for the future of the household projection model (available on the National Archive).
An overview of the methodology used to produce household projections across the four UK countries, published 27 January 2011, is available on the Welsh Government website.
Definition of a household
In the 2001 Census, for the household projections and mid-year estimates a household is defined as:
- one person living alone, or
- a group of people (not necessarily related) living at the same address with common housekeeping – that is, sharing a living room or sitting room or at least 1 meal a day
For the 2011 Census, the definition of a household was updated to reflect recent social changes and living conditions but for the 2011 interim projections it was assumed that this did not affect household formation at the aggregate level.
Projections of the number of households
The household figures for England and its local authority districts are derived by the Department for Communities and Local Government from the household projections model using sub-national population figures from the Office for National Statistics (ONS).
Generally the sub-national population projections are updated every other year following the publication of updated mid-year estimates of population but occasionally an interim set of projections are produced to meet user needs, for example after census results are published. The 2011-based projections are interim because they are based on the 2011-based interim sub-national population projections. These population projections are based on the 2011 mid-year population estimates rolled forward from the Census 2011 data and apply the demographic trends used for the previous 2010-based sub-national population projections.
An estimate of the communal establishment population is subtracted from the total population to give the private household population. These population figures, split by age, sex and marital status group, are multiplied by the projected ‘household representative rates’ that represent the proportion of the population in that category who are household representatives. These rates are based on the 1971, 1981, 1991, 2001 and 2011 censuses and Labour Force Survey data.
The breakdown of the household projections into the detailed household types is given by a projection of headship rates from the 2001 and 2011 Census.
Figures for the number of households for 2011 are derived from household representative rates applied to the ONS mid-year population estimates for 2011. They are therefore not direct estimates of the actual number of households as they are derived from modelled household representative rates.
A more detailed description of the projection methodology is available in Updating the Department for Communities and Local Government’s household projections to a 2011 base: methodology (published 9 April 2013).
Contribution to growth
Analysis of the effect of population change and household formation on household growth, presented in table 415 in live tables on household projections shows changes in the population contributed for about 98% of growth in household formation whereas changes in household formation contributed about 3% of household growth (these 2 elements do not add up to 100 because there is an interaction effect).
As the population projections are a key component of the household projections, the Office for National Statistics generally publishes a set of variant national population projections showing the effect on the population projections of different assumptions on fertility, life expectancy and net migration, and variant household projections give a broad indication of the sensitivity of the projections to these demographic assumptions.
There are no variant projections available for the interim 2011-based sub-national population projections so no variant projections have been produced for the consistent 2011 interim household projections.
In order to provide a sense of the sensitivity of the 2011-based interim household projections to changes in population, an analytical exercise has been done by applying the household formation rates from the 2011-interim household projections to the 2008-based sub-national population projections.
A quality report has been published alongside these household projections.
Historic series and archive figures
The data for 1861 to 1961 are largely based on the census figures for England and Wales, with Wales including Monmouthshire excluded to maintain an area consistent with modern England. The figures up until 1921 use families and separate occupiers and have not been adjusted to take account of the definitional change in 1921 that effectively removed the institutional population from the figures. The figure for 1939 is based on work by A. E. Holmans (see page 63, Housing Policy in Britain 1987, Croom Helm) with a pro-rata adjustment made for England using the population ratio.
Previous projections from this century have been replaced by the 2011-based interim projections but information about these can be found below:
- Household projections to 2033, England (published 26 November 2010)
- Household projections to 2031, England (published 11 March 2009)
- Household projections to 2029, England (published 16 March 2007)
- Revised household projections to 2026, England (published 28 February 2008)
The supporting live tables for the 2008-based projections (to 2033) can also be found on the National Archives.