5.1 Interpreting the projections
5.1.1 These population projections have limitations. A projection is a calculation showing what happens if particular assumptions are made. Projections for small areas like the National Parks are likely to be less reliable than those for larger areas.
5.1.2 Every two years the Office of National Statistics (ONS), in consultation with the Registrars General for Scotland and Northern Ireland, 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 the National Parks and SDP areas are based on the "principal" population projection. More information on the principal projection for Scotland and the assumptions used can be found at:
5.1.3 For the population projections by sex, age and administrative area, published on 3rd February 2010, high and low migration variant population projections were produced. High and low migration variant population projections for Scotland’s National Parks and SDP areas will be available on the General Register Office for Scotland website from 21st July 2010.
5.1.4 For SDP areas, population 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 4.)
5.2 Methodology
5.2.1 General
5.2.1.1 These population projections were produced using the demographic component method using a single year projection model – that is, a projection 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.
5.2.1.2 A more detailed description of population projections methodology can be found at:
5.2.1.3 The software used to produce the National Park and SDP area population projections is a combination of the General Register Office for Scotland’s Microsoft (MS) Excel macro population projection system and POPGROUP which is owned by the University of Manchester.
5.2.2 National Parks
5.2.2.1 The base populations for CNP and LLTNP were built up from the General Register Office for Scotland’s mid-2008 data zone populations, as explained in Section 4. A full list of the data zones that have been used to calculate the projected population of the National Parks can be found in Annex A.
5.2.2.2 For National Park areas, the fertility and mortality rates assumed in the national population projections, have been adjusted to take account of local variations observed in the five year period preceding the projection. For migration, the long- term assumptions were calculated using five year averages of migration in and out of the National Park areas. These averages were then scaled to match the migration assumptions used in the national projections. After the long-term assumption had been calculated for each area, the percentage of migrants located in each area was calculated for the long-term assumption and also in the base year using the 2007-08 migration figures. The change in the percentage of migration in each area from the base year to the long-term projection was then calculated and divided across the run- in years. The national assumptions for the run-in years were then divided up for each area – the two National Parks and the rest of Scotland. Migration assumptions are however speculative, especially for small areas like the National Parks.
5.2.3 Strategic Development Plan areas
5.2.3.1 Where a council area lies entirely 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 projections for council areas. 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 made consistent with the assumed total net migration for Fife.
5.2.3.2 For the other councils which are not entirely within an SDP area (Aberdeenshire and West Dunbartonshire) a simpler method was used. As the areas outside the SDP area boundary have small populations, it was not deemed necessary to take account of variations in fertility, mortality or migration rates within the different parts of the council areas.
5.2.3.3 A full list of data zones used can be found in Annex B.