Guest Blog: Future of Ageing 2015 series

By: Dr Jon Minton, University of Glasgow

“No one wins. One side just loses more slowly.”

This statement, made by Prez, a character on the critically acclaimed TV show The Wire, isn’t a bad way to start thinking about longevity. Of course no one can live for ever; all we can do is lose more slowly, travelling further along the life course to reach ever older ages. The life course is a series of hurdles, age specific mortality risks, each of varying heights, each of which have to be cleared before we can continue to live another year. We hope to clear more of these hurdles, travelling further into older ages, and hope to do so without sustaining too many sprains and injuries (acquiring multiple morbidities) along the way.

A life expectancy is a way of summarising many individual mortality risks faced by populations at different ages, a single number for describing the difficulty of the course. Thinking of these age specific mortality risks as hurdles of different heights, which have to be cleared before someone can travel further across the life course, then the life expectancy is when around half the people travelling the life course will have failed to clear one of these hurdles.

In England & Wales, as with everywhere else in Western Europe, each new birth cohort that enters the race has been given an easier course to travel. High hurdles that one cohort used to face at the age of 60, for example, later cohorts would instead face at the age of 61, 62, 63, and so on. These shifting mortality hurdles can be visualised like orienteering maps, with contour lines indicating specific mortality risk levels, like specific heights above sea levels. By arranging the age specific risks by birth cohort on the vertical axis and age on the horizontal dimension, we can see these hurdles to have been shifted ever further back for almost all cohorts; the only exception being the 1918 birth cohort, hobbled both by the legacy of the First World War and the Spanish Flu pandemic which wreaked havoc across the world.

Many life expectancy measures are known as period life expectancies, and are equivalent to assuming that each of these contour lines, which have been shifting steadily to older ages for each cohort, will suddenly stop shifting and become vertical lines. They make assumptions about the difficulty of life courses not yet travelled which are not compatible with more than a century of change.

The challenge for future healthcare and social provision is that we do not know how these mortality hurdles will continue to shift, and if we make the wrong assumptions, like the period life expectancy assumption, we are likely to be investing far too little in healthcare and social care provision than we should have been. By seeing how these hurdles have moved, we can at least develop a better idea about how they could continue to change in the future, and what sort of population and society we are likely to become.

Shaded contour plot of age specific mortality risks for birth cohorts born from 1850 and 1960 in England & Wales, over the age range 50 to 90 years. Reds indicate higher risks, blues lower risks, and yellows intermediate risks. Contours are labelled with log mortality risks on a base 10 scale, effectively the ‘number of zeroes’ in a mortality risk: -1.0 means a 1-in-10 risk of dying in the next year, and -2.0 a 1-in-100 risk of dying in the next year.

A period life expectancy involves assuming that the mortality hurdles will become vertical in the ‘missing’ top right corners of the maps.  (Author’s own analysis. Source: Human Mortality Database.)