Life tables consist of several functions of age, mathematically interrelated (including the number of survivors, number of decedents, and probability of dying, life expectancy), describing theoretical process of population extinction as the population ages.
The values of these functions are calculated useing of the number of deaths (in a given period, usually a year) and population by sex and age (in the middle of the given period). Life expectancy tables are used i.a. in to assess the health of the population. Trends in mortality changes, determined on the basis of life expectancy tables, are used in population projections.