Difference between revisions of "Life tables"
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=Graduated life tables ''vs.'' interim life tables= | =Graduated life tables ''vs.'' interim life tables= | ||
'''Interim life tables''' may be produced to provide statistics on period life expectancy by age and sex using extrapolation from graduated life table data. For example, in the UK interim life tables are released annually; these are based on the population estimates and deaths data for a period of three consecutive years.<ref name="ONS_interim">[http://www.statistics.gov.uk/StatBase/Product.asp?vlnk=14459&Pos=1&ColRank=1&Rank=272 UK Office of National Statistics website: page on interim life tables. Accessed 19th June 2008.]</ref> These interim life tables are based on fully graduated life tables, which are produced every decade and are based on decennial population censuses.<ref name="ONS_graduated">[http://www.statistics.gov.uk/StatBase/Product.asp?vlnk=333&Pos=1&ColRank=1&Rank=272 UK Office of National Statistics website: page on graduated life tables. Accessed 19th June 2008.]</ref> | '''Interim life tables''' may be produced to provide statistics on period life expectancy by age and sex using extrapolation from graduated life table data. For example, in the UK interim life tables are released annually; these are based on the population estimates and deaths data for a period of three consecutive years.<ref name="ONS_interim">[http://www.statistics.gov.uk/StatBase/Product.asp?vlnk=14459&Pos=1&ColRank=1&Rank=272 UK Office of National Statistics website: page on interim life tables. Accessed 19th June 2008.]</ref> These interim life tables are based on fully graduated life tables, which are produced every decade and are based on decennial population censuses.<ref name="ONS_graduated">[http://www.statistics.gov.uk/StatBase/Product.asp?vlnk=333&Pos=1&ColRank=1&Rank=272 UK Office of National Statistics website: page on graduated life tables. Accessed 19th June 2008.]</ref> | ||
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=Types of life expectancy= | =Types of life expectancy= | ||
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*cohort life expectancy | *cohort life expectancy | ||
'''Period life expectancy''' (at a given age for a certain area) is the average years a person would live, if she/he experienced that area's age-specific mortality rates for that time period throughout the whole of his or her life. Importantly, this does not make allowances for later actual or projected changes in mortality (death rates in an area are, in reality, subject to change with time). This means that period life expectancy does <u>not</u> provide the actual average number of years someone could expect to live. '''Cohort life expectancies''', however, are estimated using age-specific mortality rates. These rates allow known or projected changes in mortality in later years. These estimates of life expectancy are considered to be closer to the actual average years a person of a given age can expect to live. As an example, period life expectancy at age 65 in 2000 would be calculated using the mortality rate for that age group (65) in the year 2000, for age 66 in 2000, for age 67 in 2000 etc. Cohort life expectancy, however, at the same age would be using the mortality rates for age 65 in 2000, for age 66 in 2001, for age 67 in 2002, and so on.<ref name="ONS_Guide">[http://www.statistics.gov.uk/CCI/nugget.asp?ID=1898&Pos=1&ColRank=2&Rank=448 ONS Guide to Calculating Expectations of Life. Website. Accessed 19th June 2008]</ref> | '''Period life expectancy''' (at a given age for a certain area) is the average years a person would live, if she/he experienced that area's age-specific mortality rates for that time period throughout the whole of his or her life. Importantly, this does not make allowances for later actual or projected changes in mortality (death rates in an area are, in reality, subject to change with time). This means that period life expectancy does <u>not</u> provide the actual average number of years someone could expect to live. '''Cohort life expectancies''', however, are estimated using age-specific mortality rates. These rates allow known or projected changes in mortality in later years. These estimates of life expectancy are considered to be closer to the actual average years a person of a given age can expect to live. As an example, period life expectancy at age 65 in 2000 would be calculated using the mortality rate for that age group (65) in the year 2000, for age 66 in 2000, for age 67 in 2000 etc. Cohort life expectancy, however, at the same age would be using the mortality rates for age 65 in 2000, for age 66 in 2001, for age 67 in 2002, and so on.<ref name="ONS_Guide">[http://www.statistics.gov.uk/CCI/nugget.asp?ID=1898&Pos=1&ColRank=2&Rank=448 ONS Guide to Calculating Expectations of Life. Website. Accessed 19th June 2008]</ref> | ||
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| + | =Methodologies used to calculate life expectancy at birth= | ||
| + | Several methods may be used to calculate life expectancy at birth. For example, the UK Office for National Statistics (ONS) uses one of two methods proposed by Chiang.<ref name="chiangI">[http://www.popline.org/docs/0617/023422.html Chiang CL. The Life Table and its Applications. Malabar (FL): Robert E Krieger Publ Co, 1984.]</ref> Another commonly used method has been developed by Silcocks.<ref name="silcocks">[http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=1731769&blobtype=pdf Silcocks PBS, Jenner DA, Reza R (2001) Life expectancy as a summary of mortality in a population: statistical considerations and suitability for use by health authorities, Journal of Epidemiology and Community Health, 55, 38-43.]</ref> | ||
=Life tables and disability-adjusted life years (DALYs)= | =Life tables and disability-adjusted life years (DALYs)= | ||
Revision as of 13:22, 19 June 2008
Contents
- 1 Introduction
- 2 Using life tables to calculate population statistics
- 3 Graduated life tables vs. interim life tables
- 4 Types of life expectancy
- 5 Methodologies used to calculate life expectancy at birth
- 6 Life tables and disability-adjusted life years (DALYs)
- 7 References
- 8 Further reading, resources and links
Introduction
Life tables (or mortality tables or actuarial tables) are tables that indicate the probability that a person in a given population at an certain age will die before their next birthday. The first "life table" was drawn up in 1603 by John Graunt in his Bills of Mortality.[1] They are generally drawn up separately by sex, and may also be drawn up for subsets of a population, taking into account other factors (e.g. ethnicity etc.). These tables are used in several fields, including epidemiology, biology and actuarial science (insurance) to calculate a number of other statistics, including:[2]
- the probability of surviving any particular year of age;
- remaining life expectancy for people at different ages;
- the proportion of the original birth cohort still alive; and
- estimates of a cohort's longevity characteristics.
In the context of integrated environmental health assessment (i.e. the INTARESE method), life tables and the statistics derived from them may be used in the valuation of health impacts.
Using life tables to calculate population statistics
Figure 1 shows an interim life table for the UK for 2004-6. The notation used in the figure (and commonly used in life tables) is as follows:
- mx = is the central rate of mortality, defined as the number of deaths at age x last birthday in the three year period to which the Interim Life Table relates divided by the average population at that age over the same period.
- qx = is the mortality rate between age x and (x+1), that is the probability that a person aged x exact will die before reaching age (x +1).
- lx = is 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 three year period to which the Interim Life Table relates.
- lx = is the number dying between exact age x and (x+1) described similarly to lx, that is dx=lx-lx+1
- ex = is the average period expectation of life at exact age x, that is the average number of years that those aged x exact will live thereafter based on the mortality rates experienced in the three year period to which the Interim Life Table relates.
Graduated life tables vs. interim life tables
Interim life tables may be produced to provide statistics on period life expectancy by age and sex using extrapolation from graduated life table data. For example, in the UK interim life tables are released annually; these are based on the population estimates and deaths data for a period of three consecutive years.[3] These interim life tables are based on fully graduated life tables, which are produced every decade and are based on decennial population censuses.[4]
Types of life expectancy
There are two main types of life expectancy:
- period life expectancy
- cohort life expectancy
Period life expectancy (at a given age for a certain area) is the average years a person would live, if she/he experienced that area's age-specific mortality rates for that time period throughout the whole of his or her life. Importantly, this does not make allowances for later actual or projected changes in mortality (death rates in an area are, in reality, subject to change with time). This means that period life expectancy does not provide the actual average number of years someone could expect to live. Cohort life expectancies, however, are estimated using age-specific mortality rates. These rates allow known or projected changes in mortality in later years. These estimates of life expectancy are considered to be closer to the actual average years a person of a given age can expect to live. As an example, period life expectancy at age 65 in 2000 would be calculated using the mortality rate for that age group (65) in the year 2000, for age 66 in 2000, for age 67 in 2000 etc. Cohort life expectancy, however, at the same age would be using the mortality rates for age 65 in 2000, for age 66 in 2001, for age 67 in 2002, and so on.[5]
Methodologies used to calculate life expectancy at birth
Several methods may be used to calculate life expectancy at birth. For example, the UK Office for National Statistics (ONS) uses one of two methods proposed by Chiang.[6] Another commonly used method has been developed by Silcocks.[7]
Life tables and disability-adjusted life years (DALYs)
The DALY calculation tool designed for use in association with the INTARESE methodology uses life tables to calculate years of life lost (YLL).
References
- ↑ Graunt, J. 1603. Natural and Political Observations Mentioned in a following Index, and made upon the Bills of Mortality
- ↑ Wikipedia article for "Life table". Accessed 19th June 2008.
- ↑ UK Office of National Statistics website: page on interim life tables. Accessed 19th June 2008.
- ↑ UK Office of National Statistics website: page on graduated life tables. Accessed 19th June 2008.
- ↑ ONS Guide to Calculating Expectations of Life. Website. Accessed 19th June 2008
- ↑ Chiang CL. The Life Table and its Applications. Malabar (FL): Robert E Krieger Publ Co, 1984.
- ↑ Silcocks PBS, Jenner DA, Reza R (2001) Life expectancy as a summary of mortality in a population: statistical considerations and suitability for use by health authorities, Journal of Epidemiology and Community Health, 55, 38-43.
