Why causes of death vary from one country to another

Ask what people die from and the answer depends heavily on where they live and how old they are. A recent effort by Our World in Data to make cause-of-death data legible for a broad audience, spanning every country and more than four decades, restates a finding that demographers have described for half a century: the composition of mortality is not fixed. It moves in a fairly predictable direction as a country develops, and reading that direction is more informative than reading any single year's ranking.

The epidemiological transition

The organising idea is the epidemiological transition: the shift, accompanying a general fall in death rates, from mortality that is high, volatile, concentrated at young ages and driven by communicable diseases, toward mortality that is low, stable, concentrated at old ages and driven by non-communicable disease. In high-income settings the retreat of infectious causes over the twentieth century allowed more people to survive into the ages at which chronic conditions dominate. Cardiovascular disease and cancers now account for the largest share of deaths across most of these countries.

• Low-income settings retain a substantial burden of communicable, maternal, neonatal and nutritional causes.
• Middle-income countries frequently carry a double burden, with infectious disease still present as non-communicable disease rises.
• High-income countries sit at the far end, where chronic degenerative conditions predominate.

One transition, several speeds

The transition is a common direction, not a single timetable. The literature distinguishes a classical Western pathway that unfolded slowly over more than a century, an accelerated pathway exemplified by Japan, and a delayed or contemporary pathway followed by many countries in Africa, Asia and Latin America. Latin American countries are often described as intermediate, with circulatory diseases and cancers already prominent alongside external causes such as injury. In parts of eastern and southern Africa, HIV-related mortality reshaped the profile for a generation, a reminder that the path is neither smooth nor guaranteed to move in one direction.

How to read the numbers

Two adjustments matter before comparing countries. The first is age. A country with an older population will record more cancer and heart-disease deaths simply because more of its residents have reached the ages at which those conditions occur; age-standardised rates strip out that structural effect and are the fairer basis for comparison than crude counts. The second is data quality. Many countries lack complete vital registration, so a share of the global figures rests on modelled estimates, such as those in the Global Burden of Disease study, with wider uncertainty than a headline number implies.

A ranking of causes answers a narrower question than it appears to. The more useful question is which way a country is moving, and how fast.

Set against the broader work of this resource, the mortality transition is one half of a demographic story whose other half is falling fertility. Together they age populations, and an ageing population is precisely one in which non-communicable disease comes to dominate. Cause-of-death data, read this way, are not only a health statistic but a marker of where a country sits in its longer demographic transition. The symposium treats them as such, and the editorial method behind this brief is set out separately.

These observations describe a broad regularity, not a law. Individual countries depart from it for reasons of policy, epidemic history and measurement, and the brief is intended as a summary of the published record rather than original estimation.