Demographers’ interest in mortality and cohort attrition is reflected in life tables, which describe people’s lives as they die. Quite optimistically, these tables are called life tables and not death tables.

A life table is composed of a number of columns showing values of different life-table functions at each age, starting from birth. The basic column shows mortality rates at each age and probabilities of dying between successive years. There are other columns, which show other characteristics, such as one column showing the number of people that would be there at each age if deaths occurred according to life table, that is, if fertility balances mortality. It has another column for life expectancy that shows the average number of years left to be lived by people. Another important column shows the number of people who survived and came out of the original cohort.

There are two main types of life tables in common use: period life tables and cohort life tables.

Period Life Table

The period life table is based on mortality rates of a calendar year. The mortality rates are obtained by relating death counts at particular ages to an estimate of the population alive at those stages. The periodic life table incorporates the experience of mortality by different ages of population during a given period of time. Unless specified otherwise, life table signifies the current life table.

 Cohort Life Table

The simplest life table is the cohort life table, a registered birth cohort that is followed until all members die. This life table is constructed by relating to the number of individuals who survive a particular birthday and the number of deaths that occur during the following year or period of years.