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. 2002 Apr 20;324(7343):978.

Income inequality and population health

Better measures of social differentiation and hierarchy are needed

Richard Wilkinson 1
PMCID: PMC1122921  PMID: 11964356

Editor—Mackenbach's editorial reads like an obituary for the hypothesis that income inequality is related to population health.1 But a substantial body of evidence of such a relation has accumulated over the past 20 years, not only in the United States but also in Brazil, Russia, Taiwan, and England. Attempts to explain away this relation are rarely relevant to more than one of the many contexts in which it occurs.

The fact that health is more closely related to income in developed societies than to differences in income between them suggests effects of relative income or social status.2 But if income distribution has its main effect through differences in social status, and individual income (or education) is a proxy for individual social status, controlling income distribution for individual income makes little sense.3 It is a difference without a distinction, and more status equality is likely to improve average health.

As with individual income, the assumption that the median income of small areas measures material consumption rather than social relativities is unwarranted. Differences in median income between small areas are components of the income inequality of the larger areas. Choosing smaller areas converts variance, which would be income inequality in larger areas, into what is naively taken to be absolute income. Hence associations between income inequality and health tend to be strongest in larger areas and weakest in smaller areas, while the opposite is true of associations between median income and health.

Poor social affiliations and low status carry high population attributable risks. More unequal societies not only suffer more relative deprivation but tend to have lower rates of trust and of community involvement and—as over 40 studies show—more violence. More unequal societies will be more differentiated by social rank into relations of dominance and subordination and less able to enjoy more egalitarian and inclusive relations consistent with higher social capital and less class and racial prejudice.4 The links with violence show that inequality has psychosocial effects, and, given the powerful association between violence and other causes of death, critics should tread with caution.

Income may work better as a proxy for difference in social status in the United States than elsewhere. European differences in status ranking may be smaller and need more subtle markers. To test hypotheses that are fundamentally about differences in social status we need better measures of social differentiation and the importance of hierarchy in a society. The social dominance orientation scale might be a good place to start.5

References

  • 1.Mackenbach JP. Income inequality and population health. BMJ. 2002;324:1–2. doi: 10.1136/bmj.324.7328.1. . (5 January.) [DOI] [PMC free article] [PubMed] [Google Scholar]
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BMJ. 2002 Apr 20;324(7343):978.

Hierarchy and health are related

Stephen Bezruchka 1

Editor—Mackenbach's editorial and the accompanying four studies suggest that individual income rather than income distribution is the important determinant of population health.1-1

The studies presented do not deny a relation between hierarchy and health, but the results suggest that income distribution may not always be a good measure of that hierarchy. Non-income aspects of social rankings operating in specific cultures may overpower single economic measures such as income distribution. In addition, as the Japanese study suggests, high levels of inequality may be required before income effects are shown. Given that a perfect measure of inequality or hierarchy does not currently exist, however, the lack of such a measure does not refute the possibility of an important relation between hierarchy and health.

In Japan the poorest region (Okinawa) seems to have the lowest mortality,1-2 which is at odds with Mackenbach's individual income hypothesis. The Japanese study of Shibuya et al looked at self rated health, but this measure has been validated as related to mortality measures by only one study in Japan, compared with 13 studies of American populations.1-3 Only 0.8% of Shibuya et al's sample rated their health as poor, in contrast to studies in other populations with higher rates, such as 4.8% in an American study.1-4

The Copenhagen study confirms previous evidence. Denmark is the only rich country that has worse health, as measured by life expectancy, than the United States (the world's richest and most powerful country). Unlike the United States government, the Danish government has an official website (www.sum.dk/health/sider/print.htm) that calls attention to its relatively poor health status compared with that of other European countries and to its not having had the same secular time improvements as other countries.

This site also shows Denmark's poor life expectancy ranking, an unusual admission by a country. A higher prevalence of smoking may not be a satisfactory explanation: Japan is the world's healthiest country when ranked by life expectancy but has the highest male smoking rates of any country in the Organisation for Economic Cooperation and Development.

If individual income, rather than its distribution, is so important then why does Kerala, one of India's poorest states, have a life expectancy approaching that of the United States?1-5 The key piece of evidence required to help convince the wealthy would be that the health of the richer is better where hierarchy is decreased and everyone shares more in the fruits of society.

References

  • 1-1.Mackenbach JP. Income inequality and population health. BMJ. 2002;324:1–2. doi: 10.1136/bmj.324.7328.1. . (5 January.) [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 1-2.Cockerham WC, Hattori H, Yamori Y. The social gradient in life expectancy: the contrary case of Okinawa in Japan. Soc Sci Med. 2000;51:115–122. doi: 10.1016/s0277-9536(99)00444-x. [DOI] [PubMed] [Google Scholar]
  • 1-3.Idler EL, Benyamini Y. Self-rated health and mortality: a review of twenty-seven community studies. J Health Soc Behav. 1997;38:21–37. [PubMed] [Google Scholar]
  • 1-4.Kawachi I, Kennedy BP, Glass R. Social capital and self-rated health: a contextual analysis. Am J Public Health. 1999;89:1187–1193. doi: 10.2105/ajph.89.8.1187. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 1-5.Sen A. Development as freedom. New York: Knopf; 2000. [Google Scholar]

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