Actuarial science uses primarily two types of life tables.
First, the period life table is used to determine mortality rates for a specific time period of a certain population. The other type of actuarial life table is called the cohort life table, also referred to as a generation life table. It is used to represent the overall mortality rates of a certain population's entire lifetime.
The population selection must be born during the same specific time interval.
A cohort life table is more commonly used because it attempts to predict any expected change in mortality rates of a population in the future. A cohort table also analyzes observable mortality patterns over time.
Both types of actuarial life tables are based on actual populations of the present and educated predictions of a population's near future. Other types of life tables may be based on historical records. These types of life tables often undercount infants and understate infant mortality.