7. Definitions and limitations of the household projections

7.1 Definitions

7.1.1 The following definitions are used in this publication:

• Household: the 2011 Census definition of a household is used – one person living alone or a group of people (not necessarily related) living at the same address who share cooking facilities and share a living room or sitting room or dining area. This excludes people living in communal establishments.
• Private household population: The population living in private households, i.e. people not living in a communal establishment.
• Communal establishment: An establishment providing managed residential accommodation, such as a hospital, care home, prison, student hall of residence or barracks. ‘Managed’ means full-time or part-time supervision of the accommodation.
• Head of household: The ‘head’ of the household is normally the first person entered on the census form. The number of heads of household will be equal to the number of households.
• Headship rate: The proportion of people who head particular household types within any particular age group and Council area is known as the ‘headship’ rate.
• Children: Where children are included in a household type, the 2011 Census definition of a dependent child is used. A dependent child is anyone aged 0 to 15 in a household (whether or not in a family) or a person aged 16 to 18 in full-time education and living with his or her parent(s) or grandparent(s). It does not include any people aged 16 to 18 who have a spouse, partner or a child living in the household.
• Average household size: The average number of people in a private household, calculated by dividing the private household population by the number of households.

Figures in the tables are rounded to the nearest whole number. Therefore, the totals shown may not be equal to the sum of all the constituent parts. Calculations of additional figures based on the data in a table, for example percentage change between two years’ household numbers, have been done using unrounded numbers and then rounded accordingly.

Most of the tables included in this publication show summary figures for every five years of the projection period. Full versions of these tables, containing figures for each year, are available from the NRS website, along with detailed tables showing each household type and age group, each year, for each Council area.

7.2 Limitations

7.2.1 These household projections have limitations. A projection is a calculation showing what happens if particular assumptions are made. The household projections are trend-based and are not, therefore, policy-based forecasts of what the Government expects to happen. They are based on the population projections and, as a result, assumptions used for the population projections, such as future migration, fertility and mortality, will affect the household projections. These assumption are based on past trends. Since smaller areas tend to be affected more by migration, which is harder to predict, projections for these areas tend to be less reliable than those for areas with larger populations.

7.2.2 The household projections also rely on projecting trends in household formation from the 1991, 2001 and 2011 Censuses to 2037. They show what’s likely to happen if these trends continue into the future. There are various reasons why patterns of household formation may be different in the future, such as economic changes or the impact of new government policies, as well as imbalances between housing supply and demand. Assuming the continuation of past trends results in uncertainty in the projections, and this uncertainty increases the further into the future they are taken. Local planning policies are often intended to modify past trends and Development Plans may demonstrate departures from the projections that seem better able to fit particular local circumstances.

7.2.3 If the projections relied solely on projecting household formation trends from Census data they would be unable to reflect any changes in household formation following the 2011 Census. They would become increasingly unreliable as the start year moved further from 2011. However, the new method used for the 2012-based household projections means that any changes in household formation since the 2011 Census will be incorporated through the use of recent survey data. This will become increasingly important for future sets of projections. The 2012-based projections start roughly a year after the Census and use survey data from 2012 so they should reflect recent trends in household formation relatively well. The use of information from three censuses should also mean that longer term trends are included.

7.2.4 Projections for small groups are likely to be less reliable than those for larger groups as they are based on data from smaller numbers of people (or households).

7.2.5 This report focuses on the ‘principal projection’, that is the projection based on the assumptions that we think are most likely to occur, but it also includes sections on household projections prepared using alternative assumptions. These variant projections reflect possible effects of uncertainty in the assumptions underlying the population projections. Low and high migration variant household projections are presented in Section 5. They use the low and high migration variant population projections.

Relationship to other projections

7.2.6 These projections apply a single methodology across all Council areas. Individual areas may have a wider range of local information, based for example on local population or household surveys, on which to compile local projections. The supporting material on the NRS website should assist in providing an understanding of the basis of our projections. We are happy to provide additional supporting or background material which users would find useful in assessing and using the projections, where possible. Please contact us at [email protected]