Mortality

Human mortality is typically measured by age-specific mortality rates, such as infant mortality (before age 1), child mortality (between ages 1 and 4), adult mortality (between ages 15 and 60), and old age mortality (above age 60 or 65). The overall mortality profile can be summarized in the life expectancy at birth, which gives the average expected years of life of an individual born in a given society, assuming age-specific mortality rates in a given period as constant and given.

For most of human history, mortality is believed to have been very high, oscillating widely between 20 and 40 years, without a clear trend. During this period, mortality depended on climatic conditions, epidemics, and wars, mostly outside the control of individuals or societies. Starting in the early 19th century in some European countries, the variance and the level of mortality were drastically reduced. Throughout the second half of 19th century and first half of the 20th century, this same pattern of changes was noticed in several currently developed countries and, finally, in virtually the entire globe in the second half of the 20th century. Life expectancy at birth in developed countries rose from around 45 at the end of the 19th century to above 75 in 2000. For many developing countries, gains in life expectancy after World War II were above 20 years. The only major countervailing force to [Page 1190]this trend was the outbreak of HIV/AIDS in sub-Saharan Africa after the 1980s, with its devastating effects on mortality felt already in the 1990s.

Reductions in mortality, starting in the 19th century, mark the first stage of the demographic transition. These initial reductions have a specific composition in terms of causes of death. The changes in the cause and age distribution of mortality characterizing the progression of the demographic transition are referred to as the “epidemiological transition.” The term epidemiological transition was first coined by Abdel Omran as a description of the process of change in leading causes of death that takes place as mortality reductions progress, from infectious diseases to chronic nontransmissible diseases. Associated with this change in leading causes of death, there is also a shift in the age distribution of deaths, from mostly concentrated at younger ages to older ages, and eventually to a distribution where infant and child mortalities become relatively unimportant.

Today, the sequence of events described by Omran is not regarded as fixed but rather as a consequence of technological advances taking place at different moments in history. Jacques Vallin and France Mesle call it a “health transition” and identify three such technological shocks throughout the 20th century: the conquest of mortality from infectious diseases, which was characterized by Omran as an epidemiological transition and is still diffusing throughout the developing world; the cardiovascular revolution, which started in the mid-1960s and is still mostly restricted to the developed world; and a potential progress against mortality at very old ages, an event taking place right now and benefiting only a handful of countries.

Associated with each one of these breakthroughs is an initial period of increasing inequality, as only a few leading countries took advantage of the initial progress. Afterward, if the technology spread through other parts of the world, there could be a reduction in inequality. This sequence of events is close to completion in the case of infectious diseases, where the initial increase in international health inequality in the 19th century was followed by a reduction in inequality starting in the mid-20th century. With cardiovascular diseases, we are still observing a period of increasing international inequality.

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