Interpreting the projections
10.1 These household and population projections have limitations. A projection is a calculation showing what happens if particular assumptions are made. The household projections are based on the population projections and, as a result, assumptions used for the population projections (particularly future migration, fertility and mortality) will have an effect on the household projections. Projections for small groups are likely to be less reliable than those for larger groups.
10.2 Every two years the Office of National Statistics (ONS), in consultation with the Registrars General, produces a "principal" population projection and a number of "variant" projections, based on alternative assumptions of future fertility, mortality and migration, for the UK and its constituent countries. Projections for SDP areas are based on the "principal" population projection.
10.3 For SDP areas, population and household projections were calculated by aggregating the projections for the constituent council areas (which have already been published) and then subtracting any areas which do not form part of the SDP area such as areas which overlap with the National Parks. (For further details of the boundaries used, see Section 9)
Population projections methodology
10.4 The population projections were produced by the demographic component method using a single year projection model. A projection is made by sex and single year of age for each future year. The projection starts with population estimates for the base year, disaggregated by single year of age, sex and area. Assumptions about future fertility, mortality and migration are then used to project the future population.
10.5 Where a council area lies within an SDP area, previously published numbers of births, deaths and migrants were used. For Fife Council area, which is split between two SDP areas, variations in fertility and mortality within the Council area were accounted for using the numbers of births and deaths observed in these areas in the previous five years. This is similar to the method used to derive council projections. Long term migration assumptions for the two parts of Fife were also calculated using a similar method to that employed for the council area projections. Five year averages of migration in and out of the different parts of Fife were controlled to the assumed total net migration for Fife.
10.6 For the other councils which are not entirely within an SDP area (Aberdeenshire and West Dunbartonshire) a simpler method was used, taking no account of variations in fertility, mortality or migration rates within the council areas.
10.7 A more detailed description of population projections methodology can be found at http://www.nrscotland.gov.uk/files/statistics/projected-population-of-scotland-2006-based/j896104.htm
Population projections software system
10.8 The software used to produce these SDP area population projections is POPGROUP which is owned by the University of Manchester
Households projections methodology
10.9 Household projections are based on the population projections produced by the General Register Office for Scotland. The number of people living in private households is estimated by taking the population projections for each year and subtracting the number of people living in communal establishments, such as student halls of residence, care homes or prisons. To estimate the number of households of each type, information on household type and age group is projected forward from the 1991 and 2001 Censuses, for each household type, age group and projection area. This information is applied to the private household population to produce the basic household projections.
10.10 The household projections are trend-based, rather than policy-based forecasts. They do not take into account social and economic factors that may influence the formation of households, including policies adopted by both central and local government as well as any imbalances between housing supply and demand.
10.11 Household projections are mainly used for informing decisions about future housing need and service provision, and are used in the production of Development Plans.
10.12 A more detailed description of household projections methodology can be found at http://www.nrscotland.gov.uk/files/statistics/gros-household-projections-for-scotland-2006-based/j9646b06.htm
Household types and age groups used in the household projections
10.13 Household projections are produced for each SDP area, broken down into seven household types (based on the number of adults and children living in the household) and ten age groups, as follows:
Table C: Household types and age groups used in the household projections
Household types |
|---|
1 person households: |
1 adult: male |
1 adult: female |
2 person households: |
2 adults |
1 adult, 1 child |
3+ person households: |
1 adult, 2+ children |
2+ adults, 1+ children |
3+ adults |
Age of head of household |
|---|
16-24 |
25-29 |
30-34 |
35-44 |
45-54 |
55-59 |
60-64 |
65-74 |
75-84 |
85+ |