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Rectangularization of Mortality    

As a result of improved living conditions, of social and health policies, and medical advances, more people in developed countries can expect to an advanced age. Life expectancy has risen steadily and is now nearly 81 years in Canada (sexes combined). This places us around 7th highest in the world, an improvement from around 12th place in the early years of the millennium (source: CIA World Factbook).

A graphical way to show how improving social conditions have altered the life span is via survival curves. These show the distribution of deaths across the age range; here is a comparison of the survival curves for Canadians born in 1921 (the lowest curve), 1951 and 1991 (the upper curve).

Squaring the life expectancy curve, Canada

The fact that the curves gradually slope down from 100% illustrates a form of health disparity: in terms of age at death, and a truly equal society would seek to avoid this. Focusing on child and adolescent deaths is arguably the highest priority and would contribute more to extending average life expectancy than delaying the death of an aging person. This is the logic underlying the focus on Potential Years of Life Lost.

The effect of social improvements will be to raise the survival curve upwards and towards the upper right hand corner.  The presumed ideal would be for everyone to survive to some (as yet unspecified) age, then die relatively soon thereafter. This alteration in the shape of the survival curve is called ’squaring’ (or rectangularizing) the survival (or life expectancy) curve. Here is an example of rectangularization over time:

 

Diagram illustrating squaring the life expectancy curve and also varying levels of disability

An important debate concerns whether extending survival in this manner will mean that we also extend the lifespan of people who are sick; will adding quantity of life necessarily improve quality of life? In the diagram above, what effect will moving the red line upwards have on the blue lines? The discussion continues, but the evidence seems to be that extending survival does not necessarily entail increasing the number of years lived in a state of sickness or disability.

Updated April 3, 2013