until the age of 73.6), provided that mortality patterns observed in 2005 remained constant throughout their lifetime.įinally, another point to bear in mind is that period and cohort life expectancy estimates are statistical measures, and they do not take into account any person-specific factors such as lifestyle choices. This means that the group of 15-year-old children alive around the world in 2005 could expect to live another 63.6 years (i.e. For example, the UN estimates that the (period) global life expectancy at age 15 in 2005 was 73.6 years. Given that life expectancy at birth is highly sensitive to the rate of death in the first few years of life, it is common to report life expectancy figures at different ages, both under the period and cohort approaches. Whenever mortality rates are falling then the period life expectancy is lower than the life expectancy of the cohort born then

In general, the commonly-used period life expectancies tend to be lower than the cohort life expectancies, because mortality rates were falling over the course of modern development. We see this in the data: if you move the slider below the map forward, you’ll see that in 2019 the period life expectancy in Japan was 84.6 years, which means that mortality patterns in Japan did improve in the period 2005-2019. But if life expectancies are increasing the reality for a cohort born then is that the cohort life expectancy is higher than that period life expectancy. This means that a hypothetical cohort of infants living through the age-specific mortality of Japan in 2005 could expect to live 82.3 years, under the assumption that mortality patterns observed in 2005 remain constant throughout their lifetime. You can hover the mouse over a country to display the corresponding estimate.įor Japan, we can see that life expectancy in 2005 was 82.3 years. Let’s consider the map showing life expectancy-specifically period life expectancy-at birth in 2005. Since period life expectancy estimates are ubiquitous in research and public debate, it is helpful to use an example to flesh out the concept. Because of this, period life expectancy figures are usually different to cohort life expectancy figures. 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.

Determine life expectancy timepassages