LIFE EXPECTANCY — age discrimination
There are two different measures of life expectancy in common use:
Cohort life expectancy
Cohort life expectancy shows the probability of a person dying at each age over the course of their lifetime. It refers to a group of people with the same year of birth.
Cohort life expectancy takes into account future mortality improvement, because this is realistic (and matters when assessing longevity-related liabilities). However, this means that cohort life expectancy is subjective. This is because it requires someone to make assumptions about how future mortality might improve.
Cohort figures are often regarded as being a more appropriate measure of how long a person of a given age would be expected to live, when compared with the alternative measure known as “period life expectancy” (see below).
Period life expectancy
Period life expectancy makes no allowance for future mortality improvements and is often used as an objective measure of average current longevity. Whenever life expectancy is quoted in a statistical context, it is often period life expectancy.
Period life expectancies are a useful measure of mortality rates actually experienced over a given period. They can provide a baseline against which to benchmark cohort life expectancies. For past years they provide an objective way of comparing trends in mortality over time, between areas of a country and with other countries. Official life tables in the UK and in other countries which relate to past years are generally period life tables for these reasons.
Period life expectancies tend to be lower than cohort life expectancies, because they do not include any assumptions about future improvements in mortality rates.