Period life expectancy estimates do not take into account how mortality rates are changing over time and instead only reflects the mortality pattern at one point in time. It is the definition used by most international organizations, including the UN and the World Bank, when reporting ‘life expectancy’ figures. This approach leads to what is known as ‘ period life expectancy‘ and it is the much more commonly used life expectancy metric. Because of that statisticians commonly track members of a particular cohort and predict the average age-at-death for them using a combination of observed mortality rates for past years and projections about mortality rates for future years.Īn alternative approach consists in estimating the average length of life for a hypothetical cohort assumed to be exposed, from birth through death, to the mortality rates observed at one particular period – commonly a year. It is of course not possible to know this metric before all members of the cohort have died. You can think of life expectancy in particular year as the age a person born in that year would expect to live if the average age of death did not change over their lifetime. When we can track a group of people born in a particular year, many decades ago, and observe the exact date in which each one of them died then we can calculate this cohort’s life expectancy by simply calculating the average of the ages of all members when they died. The cohort life expectancy is the average life length of a particular cohort – a group of individuals born in a given year. One important distinction and clarification is the difference between cohort and period life expectancy. In practice, however, things are often more complicated: By definition, life expectancy is based on an estimate of the average age that members of a particular population group will be when they die.
The term “life expectancy” refers to the number of years a person can expect to live. In this section, we try to fill this gap. What does this mean exactly?ĭespite its importance and prominence in research and policy, it is surprisingly difficult to find a simple yet detailed description of what “life expectancy” actually means. Life expectancy has doubled in all world regions.
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