Why Has Mortality Declined at Such Different Rates in Different Countries?
This section explores some of the reasons mortality has declined so rapidly and at such different rates in different countries. It considers the question of whether income levels or growth rates play an important role in achieving better health or whether good policies can potentially lead to good health for low-income populations. The section concludes with a snapshot of health conditions in the world at the dawn of the 21st century.
The 20th century witnessed huge and unprecedented declines in mortality rates at all ages and in most parts of the world. Easterlin (1996) and Crafts (2000) place an emphasis on mortality transformation that is comparable to their emphasis on economic growth in their retrospectives on the unprecedented changes in the human condition during the 20th century. Understanding the sources of mortality changes is important for understanding one of the defining events of world history and also for devising policies to address the needs of the perhaps 25 percent of the world's population whose mortality rates remain far higher than those of the rest of humanity.
Several approaches shed light on the sources of mortality decline. Epidemiologists and demographers have carefully tracked specific communities for many years to assess levels of mortality and causes of death. In rural Senegal, rapid mortality decline followed introduction of interventions addressing specific conditions (Pison and others 1993).
Another approach is historical. Easterlin (1996 Easterlin (1999) examined the interplay of economic growth, urbanization, and mortality in 19th- and 20th-century Europe. He concluded that although income growth in the 19th century probably did play a role in reducing mortality (through its influence on food availability and environmental conditions), the magnitude of the effect was small. Fogel (1997) stressed the importance of increases in food availability during this period. Positive effects of income growth were partially offset by increased infectious disease transmission resulting from urbanization. Easterlin (1999) concludes that 20th-century mortality decline, which was much more rapid than that of the 19th century, had its origin in technical progress, and Powles (2001) has pointed to the importance and nature of the institutional changes required to translate technical change and economic improvements into mortality reduction. Mosk and Johansson's (1986) assessment of the interplay between income and mortality in Japan illustrates the role that adoption of public health knowledge and institutional development played in mortality decline in the country that now has the world's lowest mortality rates.
Most analysts agree that advances in science and technology have underpinned the 20th-century transformations both of income and of mortality levels. Models of economic growth rely heavily on technological progress to account for economic change (Boskin and Lau 2000; Easterly and Levine 1997; Solow 1957). Preston (1975 Preston (1980) and Fuchs (1974) provided early quantitative assessments of the central importance of technical progress in accounting for 20th-century increases in life expectancy. [Economists use the term technical progress to denote advances in knowledge that lead to new products, like vaccines, or that can inform behavior change, like knowledge of the germ theory of disease (Preston and Haines 1998).] Davis (1956) had already concluded that the unprecedented reduction in mortality in underdeveloped areas since 1940 is the result primarily of the discovery and dissemination of new methods of disease treatment that can be applied at reasonable cost. The reduction was rapid because it did not depend on general economic development or social modernization (Davis 1956, 306-7, 314). Some strands of the literature, however, attribute the high correlation of income and life expectancy at any given time to a significant causal effect of income on health (see, for example, Pritchett and Summers 1996).
Background work for this volume (Jamison, Sandbu, and Wang 2004) attempted to provide a better sense of the importance of income as a determinant of mortality by exploring the relationships among income, technical progress (or diffusion), and mortality decline. Previous econometric research either has given little emphasis to technical progress—in part simply because much of the research is cross-sectional and therefore fails to address developments over time—or has assumed the rate of technical progress or technology adoption to be constant across countries. The background work for this volume relaxed the assumption that the rate of technology adoption is constant across countries. Allowing for cross-country variation in the rate of adapting new methods resulted in weaker estimated effects of income on infant mortality rates than previously found, although education's estimated effect was robust with respect to this change.
Much of the variation in country outcomes results from the very substantial cross-country variation in the rate of technical progress—from essentially no decline in infant mortality rate caused by technical progress to reductions of up to 5 percent per year from that source. Deaton (2004) provides a complementary and extended discussion of the importance of technological diffusion for improvements in health. Many factors from outside the health sector also affect the pace of health improvement; the education levels of populations are most important. Box 1.2 briefly discusses the multisectoral nature of health's determinants. The importance of technical progress and diffusion should be viewed in this larger context.
[Box 1.2]
However technical progress or diffusion may be manifested, the large differences in its magnitude across countries suggest important effects of a country's health-related policies (Fuchs 1980; Oeppen 1999). This point bears reiterating in a slightly different way: income growth is neither necessary nor sufficient for sustained improvements in health. Today's tools for improving health are so powerful and inexpensive that health conditions can be reasonably good even in countries with low incomes.
