Further to the publication of the 2012-based national population projections for the UK and constituent countries on 6 November 2013, this release presents the data for another seven variant projections based on alternative assumptions of future fertility, mortality and migration.
National population projections are produced for the UK and its constituent countries every two years. These projections are based on the 2012 mid-year population estimates and a set of underlying demographic assumptions regarding future fertility, mortality and migration. The assumptions are based on the best statistical evidence available at the time and are agreed in liaison with the devolved administrations – Welsh Government, National Records of Scotland (NRS) and Northern Ireland Statistics and Research Agency (NISRA) - following consultation with key users of projections in each country and advice from an expert academic advisory panel.
Papers outlining the fertility, mortality and migration assumptions adopted for the 2012-based national population projections were published as part of the 6 November 2013 release.
Due to the inherent uncertainty of demographic behaviour, any set of projections will inevitably be proved wrong, to a greater or lesser extent, as a forecast of future demographic events or population structure. In addition to the principal (main or central) projection, variant projections are produced based on alternative assumptions of future fertility, mortality and migration. Some of these variant projections are intended to provide an indication of uncertainty and sensitivity to alternative assumptions; they do not represent upper or lower limits of future demographic behaviour.
Variants can be grouped into three types. Single component variants look at the effect of varying one assumption at a time from the principal projection. For example, the high fertility variant uses mortality and migration assumptions consistent with the principal projections but assumes a higher rate of fertility. Combination variants assume alternative rates for two or more of the assumptions. For instance, the young population variant assumes high fertility, low life expectancy and high net migration which results in projections with a younger age profile than the principal projection. It is also sometimes useful to prepare special case scenarios or ‘what if’ projections, to illustrate the consequences of a particular, but not necessarily realistic, set of assumptions, such as zero net migration or no change.
A full list of variants with their associated assumptions is available in Appendix A.
The principal projection and nine standard variant projections were published on 6 November. These included six possible ‘single component’ variants, two ‘combination’ variants producing the largest/smallest total population size, and one special case scenario of zero net migration. Variant and principal projections are available for the UK, England, Wales, Scotland and Northern Ireland. The principal projections are also produced for GB, and England & Wales.
The following seven additional standard ‘combination’ variant projections and special case scenarios are included in this release:
Old age structure
Young age structure
Replacement fertility projection
Constant fertility projection
No mortality improvement projection
No change projection
Long-term balanced net migration projection (available for the UK only)
After a review of the use of the variant projections in the 2010-based projections and a consultation with users, ONS decided not to produce the ‘high medium-term dependency’, ‘low medium-term dependency’, ‘stationary’ and ‘no mortality improvement & zero net migration’ variants as part of the 2012-based national projections release.
See Appendix A for the full list of variants available and their publication dates.
This projection combines assumptions of low fertility, high life expectancy and low net migration. This results in fewer babies being born, an increase in the number of older persons and a reduction in net migration which has the most impact for the younger adult age groups. This leads to a population with an older age structure than the principal projection.
This projection combines assumptions of high fertility, low life expectancy and high net migration. This results in an increase in babies being born, a reduction in the number of older persons and an increase in net migration which has the most impact for the younger adult age groups. This leads to a population with a younger age profile than the principal projection.
The other standard combination variants, high population and low population, were published with the 2012-based national population projections on 6 November 2013.
Replacement fertility is the level of fertility required for the population to replace itself in size in the long-term given constant mortality rates and in the absence of migration. Replacement level is around 2.075 in the UK, that is, women would need to have, on average, 2.075 children each to ensure the long-term ‘natural’ replacement of the population.
The replacement level is based on analysis published in an article in Population Trends 119 (186.1 Kb Pdf) in Spring 2005. Although the replacement fertility level has not been recalculated more recently, it is anticipated that any change will be minimal and unlikely to have much impact on the resulting projections.
The replacement fertility projection combines assumed replacement level fertility with the principal assumptions of mortality and migration.
This projection assumes that age specific fertility rates will remain constant at the values assumed for the first year (mid-2012 to mid-2013) of the principal projection. Although actual age-specific fertility rates for 2012/2013 were not known when the principal projection was carried out, the assumed rates were consistent with provisional estimates of total births for the year. The constant fertility projection combines assumed constant level fertility with the principal assumptions of mortality and migration.
The constant fertility projection for the UK (1.88) is only marginally lower than the long term assumption for the principal projection (1.89). Therefore, for this round of projections, results for the constant fertility variant are very similar to the principal projections.
Table 1-1 below shows the assumed long term total fertility rates assumed for the standard variants compared with assumptions based on replacement and constant fertility.
|Standard variants||Special case scenarios|
|Country||High||Principal||Low||Replacement fertility||Constant fertility|
This projection assumes that age/sex specific mortality rates will remain constant at the values assumed for the first year (mid-2012 to mid-2013) of the principal projection. Although actual age/sex specific mortality rates for 2012/2013 were not known when the principal projection was carried out, the assumed rates were consistent with provisional estimates of total deaths for the year. This projection combines assumed no mortality improvement with the principal assumptions of fertility and migration.
Table 1-2 below shows the effect on period expectation of life at birth in the year to mid-2037 with no mortality improvement compared to principal, high and low standard variants.
There is a slight difference between the no mortality improvement and low life expectancy projections. The low life expectancy projection assumes some improvement in life expectancy in the short term but no further improvement from mid-2037 onwards. The no mortality improvement projection assumes no improvement throughout the projection period.
|Standard variants||Special case scenario|
This projection uses the principal assumptions of fertility and mortality and assumes that there will be zero net migration (for every age for each sex). It therefore shows the consequences of the principal assumptions of fertility and mortality in the absence of migration, or where migration inflows and outflows are exactly equal at every age.
When compared to the principal projection, the zero net migration projection allows the impact of the principal net migration assumption on the projected population to be assessed.
This projection shows what would happen if fertility, mortality and net migration were to remain constant at current levels. It assumes the fertility rates from the constant fertility projection and the mortality rates from the no mortality improvement projection. However, given the fluctuating nature of net migration, it is much more difficult to define what is meant by the current level of net migration. The long-term assumption in the principal projections is based on analysis of recent trends and, for the UK as a whole, is similar to recent levels of net migration. So the principal migration assumptions have been used for the no change projection.
This projection assumes that net migration will decline to zero in the long-term, with in-migration and out-migration total flows being equal from the year ending mid-2034 onwards. However, unlike the zero net migration variant, it is not assumed that inflows and outflows will be equal for every age for each sex in the long-term. This variant is only produced for the UK.
Table 1-3 presents projections of the total population under the principal projection, single component variants, combination variants and special case scenarios for the UK in mid-2037, mid-2062, mid-2087 and mid-2112 and compares this to the mid-2012 estimate.
|(Mid-2012 estimate = 63,705)|
|Single component variants|
|High life expectancy||74,068||83,162||92,545||102,715|
|Low life expectancy||72,443||76,529||80,176||83,639|
|High population (High fertility, High life expectancy, High migration)||77,717||93,012||110,958||131,871|
|Low population (Low fertility, Low life expectancy, Low migration)||68,935||67,540||64,639||61,543|
|Young age structure (High fertility, Low life expectancy, High migration)||76,083||86,239||97,790||110,190|
|Old age structure (Low fertility, High life expectancy, Low migration)||70,552||74,037||76,236||78,156|
|Special case scenarios|
|No mortality improvement||70,462||73,750||77,146||80,291|
|Zero net migration (natural change only)||67,477||66,248||63,755||61,776|
|No change (Constant fertility, No mortality improvement)||70,346||73,415||76,507||79,319|
|Long-term balanced net migration||71,080||71,222||69,818||68,491|
Equivalent tables for the constituent countries and three additional measures, the percentage of the population under 16, percentage of population 65 and over and dependants per 1000 persons of working age (dependency ratios), are available in the data download.
Figure 1-1 illustrates how the total population is projected to change over the next 75 years for the principal, single component and combination variant projections.
The equivalent charts for the constituent countries of the UK can be found in appendix B.
Figure 1-2 shows the actual and projected percentage of the UK population aged 65 and over between mid-1981 and mid-2087 for the principal projection and selected standard variants.
All variants show an increase in the percentage of the total population in the UK aged 65 and over compared with the mid-2012 estimate (18 per cent). The old population variant (assuming low fertility, high life expectancy and low net migration) projects the highest percentage across all variants for this age group with 37 per cent of the UK population expected to be aged 65 and over by mid-2087.
The equivalent charts for the constituent countries of the UK can be found in appendix C.
Figure 1-3 shows the actual and projected percentage of the UK population aged under 16 between mid-1981 and mid-2087.
In contrast to the percentage of the population aged 65 and over, there is more consistency between the variants for the percentage of the population aged under 16. The young population variant (assuming high fertility, low life expectancy and high net migration) projects the highest percentage across all variants for this age group to be 20 per cent in mid-2087, compared with 19 per cent in mid-2012.
The equivalent charts for the constituent countries of the UK can be found in appendix D.
Details of the policy governing the release of new data are available by visiting www.statisticsauthority.gov.uk/assessment/code-of-practice/index.html or from the Media Relations Office email: email@example.com
These National Statistics are produced to high professional standards and released according to the arrangements approved by the UK Statistics Authority.
|Fertility||Life expectancy||Net migration||Availability|
|A||Principal projection||Principal||Principal||Principal||6 Nov 2013|
|Standard ‘single component’ variants|
|B||High fertility||High||Principal||Principal||6 Nov 2013|
|C||Low fertility||Low||Principal||Principal||6 Nov 2013|
|D||High life expectancy||Principal||High||Principal||6 Nov 2013|
|E||Low life expectancy||Principal||Low||Principal||6 Nov 2013|
|F||High migration||Principal||Principal||High||6 Nov 2013|
|G||Low migration||Principal||Principal||Low||6 Nov 2013|
|Standard ‘combination’ variants|
|H||High population||High||High||High||6 Nov 2013|
|I||Low population||Low||Low||Low||6 Nov 2013|
|K||Young age structure||High||Low||High||10 Dec 2013|
|L||Old age structure||Low||High||Low||10 Dec 2013|
|Special case scenarios|
|O||Replacement fertility||Replacement||Principal||Principal||10 Dec 2013|
|P||Constant fertility||Constant||Principal||Principal||10 Dec 2013|
|Q||No mortality improvement||Principal||No improvement||Principal||10 Dec 2013|
|J||Zero net migration (natural change only)||Principal||Principal||Zero||6 Nov 2013|
|R||No change||Constant||No improvement||Principal||10 Dec 2013|
|U||Long-term balanced net migration (UK only)||Principal||Principal||Long-term balanced||10 Dec 2013|