IJE Advance Access published online on June 5, 2007
International Journal of Epidemiology, doi:10.1093/ije/dym082
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Response: On ‘The Changing Relation between Mortality and Level of Economic Development’
Frederick J. Warren Professor of Demography, Population Studies Center, University of Pennsylvania.
E-mail: spreston{at}sas.upenn.edu
Accepted 19 March 2007
I am honoured that my 1975 article1 was thought worthy of reprinting and delighted that my own longevity curve has shifted far enough to allow me to respond to commentators. They have done an excellent job of placing the article in the context of previous and subsequent work and pointing out its strengths and weaknesses.
Inevitably, the article is to compared to the work of Thomas McKeown. Although my article and the book that included it2 were published at about the same time as McKeown's volume,3 McKeown's thesis was already well-known through the pages of Population Studies, the same journal in which my article was published. I was therefore able to become an early critic of his work.
Nevertheless, the works have much in common. As noted by Kunitz,4 they both used process-of-elimination reasoning to argue that a major factor that had been thought responsible for a large fraction of improvements in mortality was not, in fact, influential. The focus was on what was eliminated, rather than on what remained. Ironically, what was eliminated was a core variable in our own disciplines: medical technology in the case of McKeown, a physician and epidemiologist; and per capita income for someone trained as an economist/demographer. I believe that both volleys hit their primary targets, but it should be stressed that the targets were spatially and temporally limited: England and Wales 1840–1970 in the case of McKeown, and an international collection of populations between 1905 and 1965 in my case.
In the process of advocating nutritional improvements as the principal factor in mortality advances, McKeown also claimed to eliminate public health improvements as a factor. This demonstration was much less systematic and successful than his treatment of medical technologies. Many studies have demonstrated that large improvements in British mortality are associated with specific health interventions such as improvements in water supply, health education, and segregation of infectious patients.5–7 More broadly, there are scores of convincing studies showing the mortality-reducing power of improvements in water supply and sewage disposal, antimalarial campaigns, campaigns to encourage oral rehydration therapy and immunizations and so on.8
Riley,9 Kunitz,4 and Mackenbach10 note that my article has been less influential than McKeown's work, as indicated for example by citation counts (which of course include negative as well as positive citations). Kunitz has an interesting explanation of this discrepancy in terms of the political palatability of our results. Personal circumstances may have also played a role. When my article was published, I was an unknown 31-year old associate professor of sociology, much less schooled in the arts of self promotion than I am today. To the best of my knowledge, the article was never even presented at a university or professional meeting. In contrast, McKeown had been a distinguished Professor of Social Medicine at the University of Birmingham for many years when his 1976 book was published and he had a well-deserved reputation as a powerful rhetorician.11 But rhetoric is not science, and disciplinary self-reflection might be called for if, as Mackenbach suggests, the whole of McKeown's thesis became ‘conventional wisdom’ in public health and epidemiology. The disciplines of economic and demographic history have greeted his dietary claims with far more skepticism.12
The factors influencing changes in mortality vary from time to time and place to place. For example, advances in methods of treating heart disease have played a major role in mortality declines in the United States and elsewhere since 1970.13 Antibiotics, which played little role during the bulk of the decline in mortality from infectious diseases in developed countries, were far more important in many developing countries after World War II. Medical technology was not a key factor in England between 1840 and 1970, but it has been a valuable ally in health improvements in other circumstances.
The conventional triad of determinants invoked by McKeown and me—standards of living, public health initiatives and medical practice—should perhaps be supplemented by a fourth factor, personal health care practices. My studies of improvements in mortality in the United States between the 1890s and the 1930s conclude that changes in personal health care practices, stimulated by the germ theory, were instrumental in the major declines in infant and child mortality that occurred during the period.14,15 These were abetted by aggressive and highly successful government programmes, mounted in both the United States and England, designed to educate parents about proper practices: micro public health complementing macro public health. Caldwell has also stressed the importance of behavioural factors in child mortality successes and noted the centrality of women's autonomy and power as critical factors in fostering behaviours conducive to child survival.16
Wilkinson17 and Mackenbach10 usefully observe that contemporary levels of per capita income may not capture all of the economic forces relevant to health. They raise the interesting possibility that there are lags in the relation between income and mortality. These may operate over the life cycle (income levels in childhood affecting physical development in ways that manifest themselves in later life) or through wealth-generating processes whereby assets accumulate at a given level of income and exert their own influence on mortality. These are researchable topics that deserve to be pursued.
Leon18 describes the two major regional exceptions to what appeared in 1975 to be the inevitable upward march of life expectancy, reverses in Sub-Saharan Africa and in Eastern Europe. They help temper some of the optimism evident in my article, although they are not necessarily inconsistent with its claims because both regions suffered economic setbacks.
Wilkinson notes that the World Bank has documented a continuing shift in the international relation between income and life expectancy during the period subsequent to my article's publication. A recent, sweeping review of the determinants of mortality concludes that
"Cross-country data show almost no relation between changes in life expectancy and economic growth over 10, 20, or 40-year time periods between 1960 and 2000. Many countries have shown remarkable improvements in health with little or no economic growth ..."19,p.110The shift should be a cause for celebration. It means that a critically important element of human well-being can be improved without having to wait for the ponderous processes of economic growth to inch countries forward on the life expectancy/income curve. That is, of course, no reason to restrain economic growth. But, as Bloom and Canning20 note, the ‘value’ to individuals of advances in longevity is huge, by some estimates as great as the value of increases in the availability of all other goods and services combined.21 We should be grateful that this critical element of human well-being is demonstrably responsive to advances in the realm of public health and medicine.
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1 Preston SH. The changing relation between mortality and level of economic development. Popul.Stud.(Camb.). (1975) 29:231–48. Reprinted Int J Epidemiol. doi:10/1093/ije/dym075.
2 Preston SH. Mortality Patterns in National Populations. (1976) New York: Academic Press. For a closely related and somewhat more detailed effort to account for mortality change in developing countries over a similar period, see Samuel Preston, "Causes and Consequences of Mortality Change in Less Developed Countries in the Twentieth Century". In: Richard Easterlin (ed.), Population and Economic Change in Developing Countries. Chicago: University of Chicago Press, 1980. pp. 289–360.
3 McKeown T. The Modern Rise of Population (1976) New York: Academic Press.
4 Kunitz SJ. Commentary: Comments on Samuel Preston's ‘The changing relation between mortality and level of economic development.’ In: Int J Epidemiol. doi:10/1093/ije/dym076.
5 Guha S. The importance of social intervention in England's mortality decline: The evidence reviewed. Soc Hist Med (1994) 7:89–113.[Abstract]
6 Szreter S. The importance of social intervention in Britain's mortality decline c.1850-1914: A reinterpretation of the role of public health. Soc Hist Med (1988) 1:1–38.
7 Wilson LG. Commentary: Medicine, population, and tuberculosis. Int J Epidemiol (2005) 34:521–24.
8 Levine R. Millions Saved: Proven Successes in Global Health (2004) Washington DC: Center for Global Development.
9 Riley JC. Commentary: Add title. In: Int J Epidemiol.
10 Mackenbach JP. Commentary: Did Preston underestimate the effect of economic development on mortality? In: Int J Epidemiol. doi:10/1093/ije/dym080.
11 Szreter S. Rethinking McKeown: The relationship between public health and social change. Am J Public Health (2002) 92:722–25.
12 Easterlin R. How beneficent is the market? A look at the modern history of mortality. In: The Reluctant Economist—Richard Easterlin, ed. (2004) Cambridge: Cambridge University Press. 101–38.
13 Cutler D. Your Money or Your Life: Strong Medicine for America's Health Care System (2004) New York: Oxford University Press.
14 Ewbank D, Preston S. Personal health behavior and the decline in infant and child mortality; The United States, 1900–1930. In: What We Know About Health Transition—John Caldwell, ed. (1990) Canberra: Australian National University Press. 116–50.
15 Preston SH, Haines MR. Fatal Years: Child Mortality in Late Nineteenth Century America (1991) Princeton, NJ: Princeton University Press.
16 Caldwell J. Routes to low mortality in poor countries. Popul Dev Rev (1986) 12:171–220.
17 Wilkinson RG. Commentary: The changing relation between mortality and income. Commentary on Preston. In: Int J Epidemiol. doi:10/1093/dym077.
18 Leon DA. Commentary: Preston and mortality trends since the mid-1970s. In: Int J Epidemiol. doi:10/1093/ije/dym081.
19 Cutler D, Deaton A, Lleras-Muney A. The Determinants of Mortality. J Econ Perspect (2006) 20:97–120.
20 Bloom DE, Canning D. Commentary: The Preston curve 30 years on: Still sparking fires. In: Int J Epidemiol. doi:10/1093/ije/dym079.
21 Nordhaus W. The health of nations: The contribution of improved health to living standards. In: Measuring the Gains from Medical Research: An Economic Approach—Kevin Murphy, Robert Topel, eds. (2003) Chicago: University of Chicago Press. 9–40.
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