6.1.1 The results are produced by the demographic cohort component method using a single year projection model (see paragraph 6.1.2). That is, a projection is made by sex and single year of age (up to age 90 & over) for each future year. This is done for arithmetical convenience and should not be taken to imply that reliable projections can be made in such detail. However, it provides 'building blocks' which users can aggregate into age groups of their choice for the years in which they are interested. For example, the production of results in standard five year age groups (0-4, 5-9, 10-14, etc.) does not help the education planner wishing to know the size of the future population of secondary school age. Also, as some planning is done on a rolling basis (for example ten years from a moving base date), it is useful to be able to provide a projection for any future year rather than just selected years.
6.1.2 The projection starts with the population estimates for the base year, disaggregated by single year of age, sex, and area. This base population is then projected one year ahead. First, an estimate of the numbers surviving to be one year older is made by applying a series of mortality rates to give the numbers of deaths, and hence survivors, at each age. The numbers of live births in the year are produced, using fertility rates in combination with the female populations of child bearing age; and an allowance is made for infant mortality. Lastly, the expected number and age/sex structure of people entering and leaving the area is taken into account in order to cover changes in the population due to migration. These three components of population change, together with the starting population, combine to form a projection of the population one year from the base date. The process can be repeated as often as required. For each year of the projection period, it is necessary to make assumptions about the future fertility rates (to give the number of births), mortality rates (for deaths) and migration. The following paragraphs describe the base population, the small changes made to the method compared with previous projections, as well as the assumptions made in the new projections.
6.2.1 The Registrar General's mid-2010 population estimates were published in April 2011. It is these figures which are used as the base population. These cover all persons usually resident in each area, whatever their nationality. Usual residents temporarily away from home are included, but visitors are excluded. Students are taken to be resident at their term-time address. Members of Her Majesty's (HM) and non-UK Armed Forces stationed in Scotland are included; HM forces stationed outside Scotland are excluded. Short-term international migrants, who stay for less than 12 months, are excluded. Population figures relate to 30 June 2010 and ages relate to age at last birthday.
6.3.1 The software used to produce the population projections is an in-house Microsoft (MS) Excel macro system which has been developed over a number of years. The system runs on 36 'building bricks' - areas which aggregate to both Council and NHS Board areas. In order to get the base populations for the part areas the 2010 Small Area population estimates (published August 2010) are used to get the best fit to these areas. While data zones nest into Council areas they do not nest into NHS Board areas. Therefore it is assumed that the difference in the base year population estimates and the 'best fit' estimates for NHS Board areas remains constant for all 25 years of the projection period. All the projection outputs are adjusted accordingly with these small changes.
6.4.1 The projected number of births was obtained by applying age specific fertility rates to the numbers of women at each childbearing age, for each year of the projection period. In determining the fertility rates used in the national projections for Scotland, assumptions were made about the average completed family size for successive generations of women. This measure tends to be more stable over time than fertility rates for specific years (so-called period fertility rates), because of generational differences in the timing of having families. The fertility rates remain unchanged from the 2008-based projections. It was assumed that the average completed family size will continue to decline from around 1.85 children per woman for those born in the early 1960s and now reaching the end of their childbearing lives, before levelling off at 1.70 for those born in the 2000s and later. The number of births is expected to fall from around 58,900 in 2010 to around 56,500 in 2035. The resultant age specific fertility rates assumed for Scotland as a whole are given in Annex A. More information on the fertility assumptions for Scotland can be found in Annex A of the publication Projected Population of Scotland (2010-based) on the National Records of Scotland website.
6.4.2 The projected number of births by administrative area is shown in Table 4. The percentage change in the number of projected births between 2010 and 2035 by Council area is also shown in Figure 11.
Figure 11: Projected percentage change in births (2010-based), by Council area, 2010-2035
6.4.3 For local areas, the assumed national fertility rates have been adjusted to take account of local variations observed in the five year period preceding the projection. The local scaling factors used to adjust the national rates are given in Annex C.
6.5.1 The projected number of deaths each year was calculated by applying mortality rates by age and sex to the appropriate sub-populations. The national rates for the first year of the projections (2010-11) were based on autumn 2011 estimates of the numbers of deaths at each age in that period. The mortality rates for later years were based on long-term trends before 2010. Future improvements in mortality rates are based on the trend observed in the period 1961 to 2009. It is assumed that annual rates of reduction in mortality rates will tend towards a common reduction at each age of 1.2 per cent a year by 2035 for most ages. Thereafter, the mortality improvement is assumed to continue at this rate. However, it is assumed that those born in the years 1925 to 1938 (cohorts which have consistently experienced relatively high rates of mortality improvement over the last 25 years) will continue to experience higher rates of mortality improvement until they die, with assumed rates of improvement in and after 2035 rising from 1.2 per cent a year for those born after 1938 to a peak of 2.5 per cent a year for those born in 1931 and 1932 then declining back to 1.2 per cent a year for those born in 1924, and lower rates for those born earlier.
6.5.2 The difference between the expectations of life for Scotland compared to the rest of the UK has been gradually widening for males under the age of 80 since the early 1980s. There have also been increases in divergence for females since 2000. Further analysis indicated that lower rates of improvement should be adopted in Scotland for males aged 27 to 59 and 66 to 95, and for females aged 28 to 41 and 65 to 92, than for the UK as a whole. Therefore it has been assumed that the mortality rates for Scotland will continue to be higher at most ages than those for the rest of the UK, but by 2035 all improvement rates are projected to converge to the same annual rates of improvement as for the UK.
6.5.3 Based on these rates, expectation of life at birth is projected to increase from 75.8 years in 2009 to 80.9 in 2035 for men; and from 80.3 in 2009 to 85.1 in 2035 for women. The national mortality rates are shown, for selected ages and for selected years of the projection, in Annex B. Compared to the assumptions used in the 2008-based projections for Scotland, the life expectancy for men in 2035 is the same for both sets of projections, but for women it is 0.3 years lower in the 2010-based projections.
6.5.4 Similar to the fertility assumptions for local areas, the assumed national mortality rates have been adjusted to take account of local variations observed in the five year period preceding the projections. Different scaling factors were used for different age groups to reflect the fact that the variation in mortality rates between areas will itself vary between age groups. Rather than using a single scaling factor for men and another for women different scaling factors were used for age groups 0-59, 60-79 and 80+, and for men and women, meaning that up to six scaling factors were used for each area. In some smaller areas, fewer scaling factors were used as the small numbers of deaths were subject to large fluctuations. The local scaling factors used to adjust the national rates are shown in Annex C. More information on the mortality assumptions for Scotland can be found in Annex B of the publication Projected Population of Scotland (2010-based) on the National Records of Scotland website.
6.6.1 Assumptions about future levels of migration to and from Scotland were based on analysis of trends in civilian migration to and from the UK and between the four constituent countries of the UK. The principal projection assumes net in-migration of 17,500 from 2016-17 onwards; the previous 2008-based principal projection, assumed net in-migration of 12,000 per year for the long-term. In the first six years of the new projection higher net inflows are assumed, reflecting recent trends. It is assumed that in the short-term there will be a net inflow of 24,000 migrants to Scotland in 2010-2011, 25,200 in 2011-2012, 23,700 in 2012-2013, 22,000 in 2013-14, 19,000 in 2014-2015, and 18,300 in 2015-2016, before the level drops to an assumed net inflow of 17,500 for the rest of the projection period. This reflects recent increases in the number of people migrating to Scotland, after many years when net out-migration was the norm. It also includes an allowance for migrants from the A8 countries in Eastern Europe which joined the European Union (EU) in 2004.
6.6.2 For the high migration variant projection net in-migration of 28,250 is assumed for 2010-11. Migration is assumed to peak in 2011-12 at 33,700 before declining over the next five years to 26,000 from 2016-17 onwards.
6.6.3 For the low migration variant projection net in-migration of 9,000 is assumed from 2016-17 onward with higher levels (starting at 19,750 in 2010-11) assumed for the first six years.
6.6.4 More information on the migration assumptions for Scotland can be found in Annex C to the publication Projected Population of Scotland (2010-based) on the National Records of Scotland website.
6.6.5 The net migration assumptions for local areas used in the principal projection were made after consultation with local authorities. For this set of projections the new method (as discussed with the Population Projection Working Group[5] (PPWG) in October 2010) was used. The initial long-term assumptions were calculated using the same method as for the 2008-based projections, using five year averages of in and out migration between Councils within Scotland and between Councils and other countries. These averages were scaled to match the migration assumptions used in the national projections. The short-term assumptions were then calculated in the same way, using the flow data for each year from the national projections instead of only net figures as used in the past.
6.6.6 The national assumption for the run-in years was then divided up for each Council area. The assumptions for each area are shown in Annex D. It is important to remember that the sum of the local assumptions has to match the totals used in the national projections. It is also important to note that long-term migration assumptions are highly speculative.
6.6.7 For the high and low migration variant projections a similar method is used but this time the local assumptions have to match with the higher and lower totals used in the national variant projections. The higher and lower net inflows for these variants only affect moves to and from outwith Scotland and has no impact on moves within Scotland. Migration to and from an area is made up of a mixture of within Scotland and outwith Scotland migration, and the extent to which a particular area experiences more of one or the other type of migration will determine the impact of the variant projections. Figure 12 shows the Council areas which have gained large number of migrants from other countries over the past five years and which are therefore most likely to be affected by the high and low migration variants. These include Aberbeen City, City of Edinburgh, and Perth & Kinross. The trends in net migration for the previous five years are shown in Annex G. The high migration variant assumptions for each area are shown in Annex E and the low migration assumptions are shown in Annex F.
Figure 12: Migration to and from outwith Scotland and to and from other Council areas within Scotland, 2005-2010
6.6.8 Council and NHS Board area specific age/sex distributions have been assumed for the in- and out- migrant flows using information on movement of patients from the National Health Service Central Register (NHSCR) observed in the previous three years and the Community Health Index (CHI), again over the previous three years. These distributions have been made consistent with the age/sex distribution used for Scotland in the national projection.