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Life Table/Mortality Table – Overview, Construction, Example

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The life table (also called the mortality table) gives the life history of a hypothetical group or cohort as it is gradually diminished by deaths. It is a conventional method of expressing the most fundamental and essential facts about the age distribution of mortality in a tabular form and is a powerful tool for measuring the probability of life and death of various age sectors. A life table provides answers to the following questions :

  1. How will a group of infants all born at the same time and experiencing unchanging mortality conditions throughout the life time, gradually die out?
  2. When in the course of time all these infants die, what would be the average longevity per person ?
  3. What is the probability that persons of specified age will survive a specified number of years ?
  4. How many persons, out of selected number of persons living at some initial age, survive on the average to each attained age ?

The life table thus gives a summary of the mortality experience or any population groan during a given period and is a very effective and comprehensive method for providing concise measures of the longevity of that population. The data for constructing a life table is the census data and death registration data. Life tables are generally constructed for various sections of the people which, as experience shows, have sharply different patterns of mortality. Thus there are life tables constructed for different races, occupational groups, and sex. Life tables are as well constructed on a regional basis and other factors accounting for differential mortality.

Assumptions for Construction of Life Tables:

The following are a few simplified assumptions that are used in the construction of the life tables.

  1. The cohort is closed for emigration or immigration. In other words, there is no change in the census except the losses due to deaths.
  2. Individuals die at each age according to pre-determined schedule which is fixed and does not change.
  3. The cohort originates from some standard number of births, say 10,000 which is called the radix of the table.
  4. The deaths are distributed uniformly over the period (x, x +1) for each x (except for first few years). In other words, deaths are uniformly distributed between one birthday and the next.

Notations and Terminology for Life Tables:

Notations for Life Table

Construction and Example of Life Tables:

Description and Construction of Life Table

We now give an example snippet of what a mortality table looks like:

Example Snippet of a Life Table

Uses of Life Tables:

1) Actuaries in Insurance

Life tables are indispensable for the solution of all questions concerning the duration of human life. These tables, based on the scientific use of statistical methods, are the keystone or the pivot on which the whole science of life assurance hinges. Life tables form the basis for determining the rates of premiums to be paid by persons of different age groups, for various amounts of life assurance. Life tables provide the actuarial science with a sound foundation, converting the insurance business from mere gambling in human lives to the ability to offer a well-calculated safeguard in the event of death.

2) Population Projections

Life tables are used by demographers to devise measures such as β€˜Net Reproduction Rate’ to study the rate of growth of the population. They have also been used in the preparation of population projections by age and sex, i.e., in estimating what the size of the population will be at some future date.

3) For Comparison of Different Populations

Life tables for two or more different groups of the population may be used for the relative comparison of various measures of mortality such as death rate, the expectation of life at various ages, etc. Of particular interest is the comparison of the average longevity for members of a population.

4) Use by Government

Life tables are as well used by the government and private establishments for determining the rates of retirement benefits to be given to its employees or for formulating various programs for retired persons. Since a life table depicts the distribution of the people according to age and sex, it is extremely useful in planning in respect of education and for predicting the school-going population in connection with school building programs. Life tables are also used :

  1. For making policies and programmes relating to public health, by the government and public administration.
  2. To evaluate the impact of family welfare programmes on the population growth.
  3. For estimating the probable number of future widows and orphans in a community, and
  4. For computing the approximate size of future labour force and military forces, etc.

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