A life table, sometimes referred to as a mortality table or an actuarial table, is a vital demography tool. It is used to compute life expectancy at different ages within a given population and analyze patterns of mortality. A life table is a concise way to present a hypothetical cohort’s history. A life table is an aggregation of cohorts that are always specified for an amount of time and are gradually lost due to mortality at each stage.

Cohort

A cohort is a collection of people who, during a particular period of time, have similar characteristics or experience. Numerous disciplines, including sociology, epidemiology, psychology, and marketing, frequently employ this phrase. Cohorts are frequently studied over time to see how a common trait affects the members’ behaviour, results, or growth.

Example of Cohort

• Birth Cohort:. A birth cohort is a collection of people who were born in a particular period of time. It is usually in one or more distinct years.
• Death Cohort: It is also referred to as a mortality cohort. A death cohort is a collection of people who have in common the trait of passing away at a specific time.
• Marriage cohort: A group of people that were married within a specific time frame. It is like a year or a range of years, is referred to as a marriage cohort.
• Labour force cohort: A labour force cohort is a collection of people who joined or withdrew from the labour force within a particular time frame.

Importance points on Life Table

• Consider a population of one hundred thousand people born simultaneously. A life table charts their course, showing how many people survive at each age range. It also charts how many pass away, and how likely it is that they will eventually face mortality.
• Life tables are more than just lists of deaths. They go beyond and paint a complete picture of mortality in the community. They identify trends and patterns by examining the likelihood of dying at each age and identifying key points where the risk of dying may be higher or lower.
• A life table is fundamentally a probability table. It determines the qx, or the probability that a person at a certain age will pass away before reaching the following age interval.
• A common measure of a population’s longevity, life expectancy, has its origins in life tables. Life tables provide an easy-to-read assessment of the general health and longevity of a population.

History of Life table

John Graunt, the Father of Demography (1620-1674)

• Graunt created the life table in 1662, calculated the odds of survival at various ages by examining London’s Bills of Mortality, which were weekly records of fatalities.
• Although Graunt did not develop the name “demography” until 1855, his groundbreaking work established the groundwork for this important science. Achille Guillard coined the term ‘’Demography’.

The Bills of Mortality and the Worshipful Company of Parish Clerks

• The Worshipful Company of Parish Clerks produced these weekly reports, which served as the source material for Graunt’s ground-breaking investigation.
• They recorded not just the total number of fatalities but also the age ranges and causes of death, providing important information about London’s mortality trends.

William Farr and the Biometer of the Population (1807-1883)

• Farr, a prominent pioneer in 19th-century statistics, promoted the methodical display of life tables.
• He dubbed them the “biometer of the population” after realising their importance as a tool for evaluating the health of the populace.

Reed and Merrell’s Abridged Life Table (1936)

• Reed and Merrell developed a “short method” for creating reduced life tables after realising the necessity to streamline life table computations.
• Life tables are now easier to use and more useful for a larger range of demographic research thanks to this technique.

Types of Life Tables

Complete Life Table

• Offers data for each and every year of the population under study’s lifespan.
• Contains columns for each year of life expectancy (ex), probability of death (qx), number dying (dx), and number surviving (lx) for each year of life.
• We utilize complete life tables rarely in practical applications because of the large amount of data they require.
• Mainly utilised in historical analysis or research contexts where a more thorough comprehension of age-specific mortality patterns is essential

Abridged Life Table

• Groups are easier to work with and analyse since they age into bigger age intervals, usually 5 or 10 years.
• Provides information for every age range, such as the average number of people who survive (lx), die (dx), have a chance of dying (qx), and expect to live (ex) at the start of the range.
• Abbreviated life tables are the most widely used type utilised in a variety of applications because of their practicality and relative ease of use.
• Applied in actuarial computations for life insurance, pensions, and social security, as well as demographic studies and policy decisions.

Basic Assumptions

• Assumes the population being studied is closed, meaning there is no immigration or emigration during the observation period. This implies that changes in population size are solely due to births and deaths within the existing population.
• Often based on a hypothetical cohort of individuals born at the same time. This allows for tracking their mortality experience throughout their lives, even though individuals in real populations are born at different times.
• Typically, we group mortality data into age intervals of equal length (e.g., 5 or 10 years).
• Assumes that the probability of death (qx) within each age interval remains constant throughout the interval.
• The cohort originates from some standard number of births such as (1000,10000,100000 or 1000000) called Radix of the life table.
• The cohort of the persons contains member of only one sex.
• Life tables typically represent past or current mortality patterns. They may not accurately predict future trends

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