What is Life Expectancy?

By Dr Ananya Mandal, MD

Life expectancy refers to the number of years a person is expected to live based on the statistical average. Life expectancy varies by geographical area and by era. In the Bronze age, for example, life expectancy was 26 years, while in 2010, it was 67 years.

In mathematical terms, life expectancy refers to the expected number of years remaining for an individual at any given age. In formulaic terms, life expectancy is denoted  by ex, where, “e” represents the expected number of years remaining and “x” represents the person’s present age.

The life expectancy for a particular person or population group depends on several variables such as their lifestyle, access to healthcare, diet, economical status and the relevant mortality and morbidity data. However, as life expectancy is calculated based on averages, a person may live for many years more or less than expected.

The concept of life expectancy is also applied in ecological studies. Whether life expectancy is being calculated for plants, animals or humans, tables referred to as actuarial tables or mortality tables are used. Taking humans as an example, these tables can predict how likely it is that a person of a given age will die before their next birthday. From here, several points can be can be calculated, including:

  • The person’s probability of surviving to any given age
  • The life expectancy remaining for people of various ages

The oldest age any human has been known to live to is 122 years, the age reached by Jeanne Calment form France. This is referred to as the “maximum life span,” which is the maximum number of years that any human is known to have lived for.

The life expectancy in Swaziland is 49.4 years, while in Japan it is 82.6 years. However, the figure for Japan may be slightly increased due to many infant deaths being counted as stillbirths. In most developing countries such as India and many other Southeast Asian countries, the number of infant deaths is responsible for lowering the overall life expectancy. However, an article published in the “Lancet” suggested that the life expectancy in Japan may be due to factors such as diet, public health and equal opportunities.

Reviewed by , BSc

Further Reading

Last Updated: Oct 20, 2014

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