Health, inequality, and the scholars.

FEW would take exception to the idea that an improvement in the material well-being of the poor would enhance not only their living standard but their health levels as well. A number of influential recent studies, however, purport to show that inequality in income--not poverty per se--has detrimental health consequences. This "inequality hypothesis" is meant to apply to everyone, regardless of wealth or social standing, and predicts that the risk of illness depends upon whether one lives in a society that is stratified or egalitarian. Thus, according to this hypothesis, while the poor may suffer the most from inequality, the better off and even the rich suffer as well.

This is a dramatic claim--and one with potentially far-reaching implications. It extends far beyond the current paradigms upon which contemporary Western social welfare policy is premised. Current welfare policy, after all, posits that overall national health can be improved by transferring resources from society's more affluent members to its poorest and most vulnerable groups. The inequality thesis, by contrast, would seem to suggest that simply taking wealth away from the rich--and thereby reducing measured economic inequality--should in itself produce an improvement in national health. Indeed, the inequality thesis suggests that, all other things being equal, a cutback in the income of the well-to-do could be expected to improve the health status of the poor, and possibly the rich themselves--even if society were left with a lower average income level as a result of those cutbacks.

It is hard to overstate how quickly and thoroughly the inequality hypothesis has become conventional wisdom among many medical sociologists and public health scholars. It is not confined to the radical left. In Unhealthy Societies, for example, Richard G. Wilkinson of Nottingham University Medical School argues that income inequality is "one of the most powerful determinants of health" and "the most important limitation of the quality of life in modern societies." The academic world is by no means immune to fads, but the sudden popularity of the inequality hypothesis--in schools of public health, scholarly journals like the American Journal of Public Health, institutions such as the American Public Health Association, and health philanthropies like the Robert Wood Johnson Foundation--is quite extraordinary.

Additionally, the notion that income inequality is bad for health has recently surfaced in political discussions, taxpayer-funded policy research forums, and the popular media. British Prime Minister Tony Blair has stated, "There is no doubt that the published statistics show a link between inequality and health." The World Bank has dedicated an entire web page to the inequality hypothesis. In the United States, the National Institutes of Health, Centers for Disease Control and Prevention, and reporters for the New York Times and Washington Post, among others, have given favorable coverage to the subject. The hypothesis has become accepted wisdom among public health researchers and epidemiologists.

But the enthusiasm of many researchers and observers goes well beyond what might be warranted by the weight of the evidence alone. A very persuasive, if less publicly heralded, body of scholarship that challenges the inequality hypothesis is currently emerging. To get a better sense of this important debate, it is useful to examine both sides of it--the evidence adduced to support, refute, and qualify the inequality hypothesis. In addition, it is necessary to evaluate the study methodologies and data interpretation, as well as policy recommendations, of both sides. Against this background, it appears that the evidence and arguments for the inequality hypothesis are wanting in many respects, and that a number of influential scholars have jumped to policy conclusions on the basis of ideologically appealing, but technically dubious, findings.

Origins of the hypothesis

The income inequality hypothesis originated as an ad hoc explanation for the repeated observation that income inequality (the extent to which wealth is concentrated or dispersed over a population) is associated with mortality levels: The greater the degree of inequality, the higher the mortality levels in that population. From correlation was assumed causation. Antecedents of this line of academic thinking can be traced back at least to the 1970s, when income inequality emerged on the margins of the public health literature in the form of neo-Marxist jeremiads.