Population projection components of change by local authority and year
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2014 to 2015Metadata
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General description
This dataset provides the components of change involved in the calculation of the population projections for local authorities in Wales. Data cover the change between each successive projection year and relate to the change from the middle of each year to the middle of the following year. The first year's data represent the change from the base year of mid-2014 to mid-2015, through the projection period to show the change for mid-2038 to mid-2039. This is the fourth set of population projections published for the 22 local authorities in Wales.Note that the projections become increasingly uncertain the further we try to look into the future.
Also note that these figures differ from the Wales data in the national population projections produced by the Office for National Statistics because the key aim of the local authority population projections is to produce robust local authority population projections for Wales, which reflect local trends in recent years while the main purpose of the national projections is to produce robust population projections for Wales which reflect national trends in recent years.
The national projections and the local authority projections are different for two main reasons:
1. The methodology used to produce assumptions in the local authority projections are different to those used in the national projections. Some of these are due to slightly different data sources.
Also, although one set of assumptions may fit well for a national trend, using similar assumptions may not always produce feasible results for all local authority areas because of the different nature and trends between local authorities.
2. The geographical level for which the assumptions are based and applied is also important. For example, it is not appropriate to sum local rates (eg fertility) to derive a national rate, and therefore a model operating at different geographic levels (but using rates) will produce different results for the different geographic levels.
Data collection and calculation
Population projections provide estimates of the size of the future population, and are based on assumptions about births, deaths and migration. The assumptions are based on past trends. Projections only indicate what may happen should the recent trends continue. Projections done in this way do not make allowances for the effects of local or central government policies on future population levels, distribution and change.The 2014 population estimates have been used as the base for the local authority projections. The projected population is for 30 June each year. The base population estimates are based on the usually resident population. Usual residents away from home temporarily are included, but visitors are excluded. Students are counted at their term-time address. It should also be noted that the UN definition of an international migrant is used - those changing country of residence for a period of at least 12 months. Short-term migrants (eg migrant workers from Eastern European countries) are not counted in the population estimates and hence are not included in the population projections.
