1. Methodology background


 National Statistic   
 Survey name  National Life Tables QMI
 Frequency  Annually and biennially
 How compiled  Based on third party data
 Geographic coverage  UK
 Last revised  27 September 2017

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2. Important points about national life tables data

  • National life tables are a statistical tool that can be used to predict life expectancy at various ages.
  • Life expectancy is the average number of years a person is expected to live before death.
  • National (interim) life tables have been produced annually for the UK and its constituent countries since 1980 to 1982.
  • Life tables are usually constructed separately for men and for women because of their different mortality patterns.
  • There has been no change in methods or classifications within the last 10 years, and there are unlikely to be any changes in the near future.
  • In 2011 the National life tables were assessed by the UK Statistics Authority and given National Statistics status.
  • Responsibility for the production of national life tables was transferred to us in 2006 from the Government Actuary’s Department (GAD)
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3. Overview of the output

National (interim) life tables are a convenient way of analysing age-specific death rates and a standard demographic tool used to portray expectation of life at various ages. Life tables are usually constructed separately for men and for women because of their different mortality patterns. We routinely publish two types of national life expectancy, the national life table and the period and cohort life expectancy tables.

Life expectancy is the average number of years a person is expected to live before death. This is usually calculated from the time of birth, but can also be calculated from any specified age. This estimates the remaining further number of years a person, on average, can expect to live given their age.

National life tables are based on population estimates and births and deaths for a period of three consecutive years. The three-year rolling averages are used to smooth fluctuations due to exceptional events, for example, a “flu” epidemic.

Period and cohort life expectancy tables are produced biennially based on the assumptions for future mortality from the national population projections (NPP). These tables give historic and projected life expectancies by single year of age and sex, from 1981 to the NPP base year and then 50 years into the future. The historic life expectancies are based on unsmoothed calendar year mortality rates and the projected mortality rates from the national population projections.

Life expectancy figures provide users with an indicator of the health of the nation, which can be used to inform policy, planning and research in both public and private sectors in areas such as health, population, pensions and insurance. Internally, we use the national life tables to calculate disability free life expectancy and healthy life expectancy.

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4. Output quality

This document provides a range of information that describes the quality of the data and details any points that should be noted when using the output. We have developed Guidelines for measuring statistical quality; these are based upon the five European Statistical System (ESS) quality dimensions. This document addresses the quality dimensions and important quality characteristics, which are:

  • Relevance
  • Timeliness and punctuality
  • Coherence and comparability
  • Output quality trade-offs
  • Assessment of user needs and perceptions
  • Accessibility and clarity

More information is provided about these quality dimensions in the sections that follow.

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5. About the output

Relevance

(The degree to which statistical outputs meet users’ needs.)

Life expectancy figures provide users with an indicator of the health of the nation and mortality throughout the life cycle. They can be used to inform policy regarding state pension age, planning and research in both public and private sectors in areas such as health, population, pensions and insurance. We use national life tables in the methodologies used to calculate disability-free life expectancy and healthy life expectancy. They are also used to inform the assumptions of future mortality for the national population projections.

Other organisations that use life tables include:

Other government departments:

  • Government Actuary’s Department
  • Department for Work and Pensions
  • Department of Health and Health Authorities
  • National Records of Scotland, Northern Ireland Statistics and Research Agency, and Welsh Government
  • HM Treasury

Non-government organisations:

  • universities – academics and students
  • news media
  • financial advisors and consultants
  • insurance companies and actuarial professions
  • the general public

Period life tables are calculated using age-specific mortality rates for a given period, with no allowance for any actual or projected future changes in mortality. This means that period life expectancy at birth for a given time period and area is an estimate of the average number of years a new born baby would survive if they experienced the particular area’s age-specific mortality rates for that time period throughout their life. The period life expectancy is therefore a useful measure of mortality rates over a given period and provides an objective means of comparison of the trends in mortality over time and with other countries.

Cohort life tables are calculated using age-specific mortality rates which allow for known or projected changes in mortality in later years.

Period and cohort life expectancies for each year are produced every two years from national population projections.

The expectation of life figures shown in the life tables are period life expectancies.

Users and their needs are identified when they contact us about life tables. An email address is available for population statistics related enquiries pop.info@ons.gsi.gov.uk. Enquiries related to life tables are noted and recorded along with any telephone enquiries. The life table is a long-established output with a relatively specialised user base.

Life tables are published on our website and are freely available to all.

Timeliness and punctuality

(Timeliness refers to the lapse of time between publication and the period to which the data refer. Punctuality refers to the gap between planned and actual publication dates.)

The national life tables provide the user with life tables in the intercensal period enabling up-to-date analysis of life expectancy. This is important for tracking progress against health targets and pension analysis.

National life tables are usually published annually at the end of September. For a particular calendar year they become available around nine months after the end of the reference year. This time lag reflects the availability of the data sources, and the time required to process the data and calculate the life tables. The publication date for life tables is determined by the availability of the mid-year population estimates and the registration of births and deaths data.

Period and cohort life expectancy tables are timed to be released one to two months after the publication of the national population projections. National population projections are usually published biennially.

For more details on related releases, the UK National Statistics Publication Hub is available online and provides 12 months’ advance notice of release dates.

The publication of the life tables would only be later than the planned date if essential data used to calculate the tables were not available or delayed, for example the rebasing of mid-year population estimates to the latest census, or if substantial problems were encountered with the processing systems used to calculate the tables. In previous years the planned publication date, as entered into the National Statistics Publication Hub Release Calendar has always been met.

In the unlikely event of a change to the pre-announced release schedule, public attention will be drawn to the change and the reasons for the change will be explained fully at the same time, as set out in the Code of Practice for Official Statistics.

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6. How the output is created

A life table is purely a hypothetical calculation. It is a statistical tool typically used to portray expectation of life at various ages. The basic assumption is that a given cohort of births (100,000 born in a given year) are subject, as the survivors pass through each year of age, to the mortality rates prevailing for each age.

Period life tables deal with current mortality rates only and no assumptions are made about future changes. The mortality rates for each age are used to calculate how many of the cohort will reach each year of age until eventually all members of the cohort have died. This enables the total number of years lived by the cohort to be calculated. When this total is divided by the number of persons in the cohort (100,000), the result is the average number of years lived in the cohort or the mean expectation of life at birth. The total number of years lived by the cohort from any given age can also be calculated and when divided by the number of survivors in the cohort entering upon that year of age, the figure obtained is the expectation of life in years for those persons.

Cohort life tables are calculated using age-specific mortality rates which allow for known or projected changes in mortality in later years. A cohort life table provides mortality rates that vary over time for each age. For example, cohort life expectancy at age 65 in 2012 would be worked out using the mortality rate for age 65 in 2012, for age 66 in 2013 for age 67 in 2014 and so on. This uses observed mortality rates in 2012 and projected mortality rates from 2013. Therefore, cohort figures are regarded as a more appropriate measure of how long a person of a given age would be expected to live on average than period life expectancy.

Life tables are usually constructed separately for males and females because of their very different mortality patterns. A life table contains:

mx
The central rate of mortality, defined as the average annual number of deaths at age x last birthday in the year or years to which the life table relates divided by the average population at that age over the same period.

qx
The mortality rate between age x and (x + 1), that is the probability that a person aged x exactly will die before reaching age (x + 1).

lx
The number of survivors to exact age x of 100,000 live births of the same sex who are assumed to be subject throughout their lives to the mortality rates experienced in the year or years to which the life table relates.

dx
The number dying between exact age x and (x + 1) described similarly to lx , that is dx = lx - lx+1 .

ex
The average period expectation of life at exactly age x that is the average number of years that those aged x exactly will live thereafter based on the mortality rates experienced in the year or years to which the life table relates.

The method of constructing a life table is widely available in demographic text books, for example, Hinde A, Demographic Methods.

The national life tables we publish are calculated using a well-established and internationally recognised methodology. The data used at the national level are sufficiently reliable for single year of age to be used throughout. The life tables are thus “complete”. We calculate the life tables for the UK and each of the constituent countries, so each set (national life tables, decennial life tables and the period and cohort life expectancy tables) are comparable across and within the UK.

The life tables are based on the mid-year population estimates and corresponding data on births, infant deaths and deaths by individual age from those years (the calculation of infant mortality also requires monthly births data for the year before the three year period). The life tables use data for a period of three consecutive years. This helps to reduce the effect of annual fluctuations in the number of deaths caused by seasonal events such as a flu epidemic. A guide to calculating interim life tables is available on our website. The decennial life tables are fully graduated (smoothed) and are published with release-specific documentation on methods and results, all this information is available on our website.

Information on the assumption-setting process for future mortality patterns are outlined in:

4. Mortality assumptions: 2014-based national population projections

Quality Reports for data used in the calculation of life tables are available for births, deaths, mid-year population estimates, population estimates of the very old and population projections.

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7. Validation and quality assurance

Accuracy

(The degree of closeness between an estimate and the true value.)

We use well-established and internationally recognised methods to calculate national life tables. They are “complete” life tables because single-year age groups are used throughout, as the data used at national level are sufficiently reliable to do so. This is preferable to the “abridged” life table where some data are lost in the grouping of ages. Abridged life tables are used at the local area level. These are more suitable for calculating sub-national life expectancy than complete life tables due to small numbers of deaths by single year of age, particularly among younger age groups and in smaller areas. Sub-national life expectancy and the associated quality report are published on our website.

There has been no change in methods or classifications within the last 10 years and there are unlikely to be any changes in the near future. Where there has been a revision in the input data, we have checked that this would not imply any revision of practical significance to users. There have been revisions to the life tables between 2000 to 2002 and 2010 to 2012 following the rebasing of the mid-year population estimates to the 2011 Census results. Any revisions observe the Population Statistics Revisions Policy.

Broader quality assurance of the period and cohort life expectancy figures is provided by expert discussion of mortality assumptions (which also feed into the national population projections). The expert advisory group was set up following a recommendation of the National Statistics Quality Review Series No. 8 – National Population Projections: Review of Methodology for Projecting Mortality specifically for this purpose. The minutes of meetings and responses to the expert questionnaire have all been published on our website.

Coherence and comparability

(Coherence is the degree to which data that are derived from different sources or methods, but refer to the same topic, are similar. Comparability is the degree to which data can be compared over time and domain for example, geographic level.)

Like national life tables, sub-national life expectancy figures are calculated for three-year rolling periods. However, life expectancy statistics for regions, counties and local areas in the UK are calculated annually using abridged (based on five-year age groups) life tables. These are more suitable for calculating sub-national life expectancy than complete life tables (based on single year of age as in the national life tables) because of small numbers of deaths by single year of age, particularly among younger age groups and in smaller areas. Life expectancy figures are also calculated using the abridged method at the national level for comparison purposes with the local area statistics however, these two sets of national life expectancy figures may differ slightly (usually by around plus or minus 0.1 years).

There have been no changes in methods or classifications within the last 10 years. We use internationally recognised methodology in the construction of life tables. We calculate the life tables for the UK and each of the constituent countries, so are comparable across and within the UK.

Tables 1 and 2 show international comparisons, using period life expectancy at birth, at age 65 and at age 85 for males and females respectively, for a selection of countries. The countries are ordered by life expectancy at birth.

It should be noted that life expectancies were not always available for 2016 for each of the selected countries. Where this was the case the most recent life expectancy estimate was used. The years to which each country’s life expectancy refers should be considered, as direct comparisons cannot be made. The reference years can be found in Tables 1 and Table 2.

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8. Concepts and definitions

(Concepts and definitions describe the legislation governing the output and a description of the classifications used in the output.)

We use internationally recognised methodology in the construction of life tables. The method of constructing a life table is widely available in demographic text books, for example, Hinde A, Demographic Methods and Newell C, Methods and Models in Demography.

The life table is a method of deriving measures which are representative of average life expectancy prevailing at a given time. It is a purely hypothetical calculation. It is a statistical tool typically used to portray expectation of life at various ages.

A life table describes the course of mortality throughout the life cycle. The components of a life table are described in section 6.

Life expectancy

Life expectancy is the average number of years a person has before death, conventionally calculated from the time of birth, but can also be calculated from any specified age. Life expectancies can be calculated for any age, giving the remaining life expectancy that is, the further number of years a person can on average expect to live given the age they have attained.

Period life expectancy

Period life expectancy at a given age for an area is the average number of years a person would live, if he or she experienced the particular area's age-specific mortality rates for that time period throughout his or her life.

Cohort life expectancy

Cohort life expectancy makes allowances for mortality improvements. These are calculated using age-specific mortality rates which allow for known or projected changes in mortality in later years. For example, cohort life expectancy at age 65 in 2000 would be worked out using the mortality rate for age 65 in 2000, for age 66 in 2001 for age 67 in 2002 and so on. Therefore, cohort figures are regarded as a more appropriate measure of how long a person of a given age would be expected to live on average than period life expectancy.

The cohort life expectancy answers the question “For a group of people aged x in a given year, how long would we expect them to live, on average, if they experienced the actual or projected future age-specific mortality rates not from the given year but from the series of future years they survive?”

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9. Other information

Output quality trade-offs

(Trade-offs are the extent to which different dimensions of quality are balanced against each other.)

Interim life tables are not fully graduated life tables. Three-year rolling averages are used to smooth fluctuations due to exceptional events, for example a flu epidemic. They are known as interim life tables since fully graduated life tables have also been prepared every 10 years (decennial life tables), based on data around a census year.

Birth and death registration data necessary for the calculation of mortality rates (the major component of a life table) are from high quality administrative sources based on a statutory obligation to register these events. Our official mid-year population estimates are used as the denominator in the calculation of mortality rates and these estimates are the best estimates of the UK population available.

Existing sources of data are used, namely: birth and death registrations, mid-year population estimates and estimates of the very old, so there is no additional cost or burden in the collection of statistics. These data are the best possible sources for the calculation of life tables.

Assessment of user needs and perceptions

(The processes for finding out about uses and users, and their views on the statistical products.)

Users and their needs are identified when they contact us about life tables. These queries are noted and recorded along with any telephone enquiries. The life table is a long-established output with a relatively specialised user base.

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10. Sources for further information or advice

Accessibility and clarity

(Accessibility is the ease with which users are able to access the data, also reflecting the format in which the data are available and the availability of supporting information. Clarity refers to the quality and sufficiency of the release details, illustrations and accompanying guidance.)

The national life tables are published on our website and are freely available to all. The accompanying statistical bulletin, user guides, quality reports about input data and methodology papers are all accessible on our website. The life tables are Excel spreadsheets available to download and all other reports are in HTML and PDF formats.

Our recommended format for accessible content is a combination of HTML webpages for narrative, charts and graphs, with data being provided in usable formats such as CSV and Excel. Our website also offers users the option to download the narrative in PDF format. In some instances other software may be used, or may be available on request. For further information please refer to the contact details at the beginning of this document.

For information regarding conditions of access to data, please refer to these links:

In addition to this Quality and Methodology Information, basic quality information relevant to each release is available in the Quality and Methodology notes of the relevant statistical bulletin.

Useful links

Population estimates

Estimates of the very old

Guide to calculating estimates of the very old

Live births and stillbirths

Death registrations

Health expectancies at birth and at age 65 in the UK

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Contact details for this Methodology