Difference between revisions of "Life tables"
m |
m (→Using life tables to calculate population statistics) |
||
| Line 11: | Line 11: | ||
=Using life tables to calculate population statistics= | =Using life tables to calculate population statistics= | ||
The notation most commonly used in life tables is as follows: | The notation most commonly used in life tables is as follows: | ||
| − | *'''''m<sub>x</sub>''''' = 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. | + | *'''''m<sub>x</sub>''''' = 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. |
*'''''q<sub>x</sub>''''' = 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)'''''. | *'''''q<sub>x</sub>''''' = 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)'''''. | ||
*'''''l<sub>x</sub>''''' = 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. | *'''''l<sub>x</sub>''''' = 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. | ||
Revision as of 11:33, 19 June 2008
Contents
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
The notation most 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]
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.[5] Another commonly used method has been developed by Silcocks.[6]
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.
- ↑ 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.
