4. Mortality Assumptions, 2010-Based National Population Projections

Introduction

The 2010-based national population projections are based on the estimated population at the middle of 2010 and a set of demographic assumptions about future fertility, mortality and migration based on analysis of trends and expert advice.

This report provides detailed information on the principal and variant mortality assumptions used in the 2010-based national population projections. The long term mortality assumption projects life expectancy at birth to be 83.3 years for men and 87.0 years for women in 2035 based on the mid-year mortality rates. Also published today are the 2010 based period and cohort life expectancy figures for 1981-2060 based on calendar year mortality rates.

Principal assumptions

The mortality rates for the first year of the projection, mid-2010 to mid-2011, are based on the best estimates that could be made in the autumn of 2011 of the numbers of deaths at each age in 2010-11. Assumed improvements in mortality rates after 2010-11 are based on trends in mortality rates before 2010.

The assumptions used in the 2010-based projections are that annual rates of improvement would converge to 1.2 per cent for most ages in 2035 (the 25th year of the 2010-based projections), and remain constant at 1.2 per cent a year thereafter. However, those born after 1924 and before 1939 have exhibited greater rates of improvement over the last 25 years than those born on either side. There is currently no evidence that these differentials are declining. Similar cohort effects seen in other countries suggest that these differentials may persist well into the oldest ages.

As a result, it is assumed that these cohorts will continue to experience higher rates of improvement after 2035 with the assumed rate of improvement in 2035 and beyond rising from 1.2 per cent a year for those born in 1924 to a peak of 2.5 per cent a year for those born in 1931 and 1932 and then declining back to 1.2 per cent a year for those born in 1939 and later. For those born before 1924, rates of improvement are assumed to be lower than 1.2 per cent in 2035.

These are the same assumptions for the rates of mortality improvement in the target year as those used in the 2008-based projections (where the target year was 2033) for those born before 1940; for those born in 1940 and later the proposed improvement rates in the target year are higher than assumed in the 2008-based projections.

Over the 40-year period 1969-2009, the average annualised rate of improvement in mortality rates in the UK has been approximately 1.8 per cent for males and a little over 1.4 per cent for females. These rates of improvement are derived from aggregate mortality rates for ages 0 to 99 calculated using the 2001 population estimates for the UK as the standard population. The rate of improvement over the latter half of this period was higher than over the first half, particularly for males.

This appears to be partly due to differential trends in smoking behaviour between males and females. Relatively higher numbers of men have now given up smoking and mortality rates for males at older ages have shown large rates of improvement in recent years.

The average annual rate of improvement over the whole of the 20th century was around 1.2 per cent for both males and females although the improvement rates vary by age. There is considerable debate as to whether the impact of future technical, medical and environmental changes will have a greater or lesser effect on improvements in mortality in the future than they had over the 20th century.

The transition from current rates of mortality improvement by age and gender, derived from recent trends, to the assumed rates of 1.2 per cent to 2.5 per cent in 2035 is not assumed to take place linearly, but more rapidly at first for males and less rapidly for females. There is growing evidence of generational effects for those born after 1940. Thus, in these projections, convergence to the assumed rate of improvement in 2035 has been done by cohort for all those born before 1960.

For those born in 1960 and later, for whom there is little evidence of generational effects, the changes in the rates of improvement to the target rate are projected by calendar year.

The rates of improvement after 2035 are assumed to remain constant (by cohort or by age, as described above) at the rate assumed in 2035 for each year thereafter. Taking account of the generally higher rates of improvement assumed prior to 2035, this produces average annualised rates of mortality improvement of around 1.4 per cent for males and 1.5 per cent for females over the projection period to 2085 (75 years), which are around 0.1 per cent a year higher than those experienced over the past 75 years for males and 0.2 per cent a year higher for females.

The same future rates of improvements have been assumed for all countries of the UK except for some differences (generally, slightly smaller improvements) in the period to 2035 at some ages for males and females in Scotland, as has been done in recent past projections.

In 2035, period expectation of life at birth for the UK is around 0.1 years lower than in previous projections for males and 0.2 years lower for females compared to the previous projections.

These differences are mainly due to the age-specific mortality rates for 2010 being assumed to be higher and the rates of mortality improvement between 2010 and 2011 assumed to be lower at many ages below 90 compared to those projected for the same period in the 2008-based projections. Over the early years of the projections these counterbalance the assumption of higher rates of mortality improvement at most ages in 2035.

Period expectations of life at birth and at age 65, based on the projected mortality rates, are shown for selected future years in Table 4-1. A summary of the assumed percentage rates of mortality reduction for some specimen years and ages is shown in Table 4-2.

Table 4-1

Period expectation of life at birth and at age 65 according to mortality rates assumed for selected years

Table source: Office for National Statistics

Table 4-2

Assumed percentage reduction in death rates, mx, between calendar years for England, Wales and Northern Ireland

Table source: Office for National Statistics

Table notes:

1. Projections are made by calendar year. Except figures in bold where, projections are made by cohort.

Table 4-3

Assumed percentage reduction in death rates, mx, between calendar years for Scotland

Table source: Office for National Statistics

Table notes:

1. Projections are made by calendar year. Except figures in bold where, projections are made by cohort.

Figure 4-1 shows the actual and projected period expectation of life at birth for males and females in the UK between 1981 and 2085. The equivalent figures for the constituent countries of the UK can be found in the Appendices A to D.

Figure 4-1

Period expectation of life at birth, United Kingdom, 1981-2085

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Figures 4-2 and 4-3 show actual and projected period expectations of life at birth for males and females for the constituent countries of the UK between 1981 and 2060.

Figure 4-2

Actual and projected period expectation of life at birth, males, 1981-2060

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Figure 4-3

Actual and projected period expectation of life at birth, females, 1981-2060

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Assumptions for mortality variants

Current annual improvements in mortality rates vary considerably by age and sex. For mortality, it is assumed that for most ages these improvements will gradually converge to common 'target rates' of improvement, at each age and for both sexes, by the year 2035, and continue to improve at that constant rate thereafter. However, it is also assumed that those born in the years after 1924 and before 1939 (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 than the rest of the population.

The target rate assumptions are as follows:

• High variant: 2.4 per cent annual improvement at 2035, thereafter annual improvement remaining at 2.4 per cent. For those born between 1925 and 1938 rates of annual improvement in and after 2035 will rise to a peak of 3.7 per cent a year for those born in 1931 and 1932 and then decline back to 2.4 per cent a year for those born in 1939 or later.

• Principal projection: 1.2 per cent annual improvement at 2035, thereafter annual improvement remaining at 1.2 per cent. For those born between 1925 and 1938 rates of annual improvement in and after 2035 will rise to a peak of 2.5 per cent a year for those born in 1931 and 1932 and then decline back to 1.2 per cent a year for those born in 1939 or later. 

• Low variant: 0 per cent annual improvement at 2035, thereafter mortality rates remaining constant. For those born between 1925 and 1938 rates of annual improvement in and after 2035 will rise to a peak of 1.3 per cent a year for those born in 1931 and 1932 and then decline back to 0 per cent a year for those born in 1939 or later.

Table 4-4 shows period expectation of life at birth in 2035 that result from the assumptions above.

Table 4-4

Period expectation of life at birth in 2034-35, for the standard variants

Table source: Office for National Statistics

Figure 4-4 shows actual and projected period expectation of life at birth for the UK between 1981 and 2085 for the principal projection and the high and low variants. The equivalent figures for the constituent countries of the UK can be found in Appendices A to D.

Figure 4-4

Actual and projected period expectation of life at birth, United Kingdom

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Background notes

1. 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: media.relations@ons.gsi.gov.uk

   These National Statistics are produced to high professional standards and released according to the arrangements approved by the UK Statistics Authority.

Appendix A: England charts

Figure 4-1

Period expectation of life at birth, England, 1981-2060

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Figure 4-4 

Actual and projected period expectation of life at birth, England, 1981-2085

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Appendix B: Wales charts

Figure 4-1

Period expectation of life at birth, Wales, 1981-2060

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Figure 4-4

Actual and projected period expectation of life at birth, Wales, 1981-2085

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Appendix C: Scotland charts

Figure 4-1

Period expectation of life at birth, Scotland, 1981-2060

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Figure 4-4

Actual and projected period expectation of life at birth, Scotland, 1981-2085

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Appendix D: Northern Ireland charts

Figure 4-1

Period expectation of life at birth, Northern Ireland, 1981-2060

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Figure 4-4

Actual and projected period expectation of life at birth, Northern Ireland, 1981-2085

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