Exploring the relationships between income inequality, socioeconomic status and health: a self-guided tour?

Jennifer M Mellora and Jeffrey Milyob

a College of William and Mary, Department of Economics, PO Box 8795, Williamsburg, VA 23187-8795, USA. E-mail: jmmell{at}wm.edu
b Harris School of Public Policy, University of Chicago, 1155 East 60th Street, Chicago, IL 60637, USA.

Income, Socioeconomic Status and Health: Exploring the Relationships. JA Auerbach, BK Krimgold (eds). Washington DC: National Policy Association, 2001, pp. 161, $20.00. ISBN: 0-89068-154-6.

Improving Health: It Doesn’t Take A Revolution. JA Auerbach, BK Krimgold, B Lefkowitz. Washington DC: National Policy Association, 2000, pp. 30, $10.00 ISBN: 0-89068-153-8.

While the US enjoys a standard of living unmatched by many nations around the world, the successes of this strong economic standing are not enjoyed by all. Income and wealth are unevenly distributed; further, widespread health disparities have been documented across racial, ethnic, and socioeconomic status (SES) groups. These facts form the basis for two reports recently published by the National Policy Association's Academy for Health Services Research and Health Policy. Income, Socioeconomic Status and Health: Exploring the Relationships, edited by James A. Auerbach and Barbara Kivimae Krimgold, is a collection of 12 papers presented at an April 2000 conference of a similar name (the book title refers to ‘income’ while the conference title gave top-billing to ‘income inequality‘). Improving Health: It Doesn’t Take A Revolution, a monograph authored by Auerbach, Krimgold and Bonnie Lefkowitz, summarizes the introduction and conclusion to the larger collection. Consequently, we limit our comments to the edited volume.

This collection of essays has two purposes. The first, as expressed in the book's foreword, is to ‘put the extent and severity of these disparities before America's leaders’. This more narrow goal is largely met. However, the broader goal of this volume is to describe the links from income inequality to health inequality and to discuss the policy implications of these links. On the question of whether the volume meets this objective, we feel the answer is ‘no’.

The volume is organized in three parts. The first set of five chapters includes contributions from several prominent researchers in the field of public health which detail studies on the relationships between measures of SES and health. Each author provides a broad overview of either the link between income and health, or the link between income inequality and health. These reviews are to be commended for their coherent and consistent (albeit one-sided) introduction to the public health perspective on this literature. The second third of the volume consists of five chapters reviewing options for policy makers interested in reducing health inequalities. These authors point to steps such as tax and transfer policies (which follow directly from the conclusions of research studies presented in Part I), as well as policies to address health inequalities by race, labour market and workplace policies, and steps to improve access to and quality of medical care. The last third of the volume features two contributed chapters and a conclusion that provide both summary and calls for future actions, and, to some degree, critical commentary.

The volume does best from the standpoint of presenting a set of descriptive facts about health disparities and income disparities in the US, and documenting numerous research studies on the determinants of health status and the link between SES and health. Examples of this contribution include the chapter by David R Williams which provides a well-documented exposition of racial disparities in health, their possible causes, and some steps that could be taken to rectify them, and the contribution by Nancy E Adler, who outlines a number of possible explanations for the observed correlation between SES and health. The volume also provides a clear introduction to a relatively new measure of SES—income inequality—and provides citations to a vast number of studies on the link between income inequality and health and possible pathways responsible for this link (see chapters by Ichiro Kawachi, Bruce P Kennedy, and Richard G Wilkinson). A third strength of the volume is the inclusion of data and experience from other countries that are grappling with similar disparities in health, namely Canada and the UK. Katherine S Newman's chapter on the UK's Acheson Report is a particularly noteworthy example of the use of international experience to guide US research and policy recommendations.

Thus, in terms of providing America's leaders (and researchers) with a basic introduction to health and economic disparities and an international context in which to view them, the volume hits its mark. Yet, it falters when it comes to guiding policy makers and researchers through the maze of facts and findings found in the scientific literature. While it is true that the volume's summary statistics and correlations help to provide policy makers with some relevant background, the book fails to provide policy makers with guidance about the extent of causal relationships. This being absent, it is difficult to assess the efficacy of various policy proposals. In terms of providing evidence even for or against the existence of causal relationships from income inequality or SES and health, the volume is not very persuasive. In particular, the messages it sends are inconsistent, and at times contradictory. Nowhere is this more apparent than on the issue of the causality from income inequality to health. For example, one contributor writes ‘it would be foolhardy to say that inequality causes sickness’ (Ch. 7, p. 88), while elsewhere another contributor asserts that ‘the extent of income inequality also appears to be one of the most powerful determinants of health’ (Ch. 3, p. 29). Certainly contrasting views are acceptable; moreover conflicts can be informative—especially in a relatively new area of research. However, the volume's editors barely acknowledge that such conflicts exist, and make little effort to glean insights from differing views. It seems incomplete not to include additional commentaries, or detailed information on the ‘other’ side, or extended discussions of these contrasts in the volume.

The volume's inconsistency is particularly problematic in the mismatch between the introduction and Part I (research) contributions as compared to the Part II (policy options) contributions. The introduction largely focuses on the conclusion that income inequality causes poor health. The research papers for the most part support this assessment of the literature. Although most contributors are cautious and do not explicitly state that income inequality causes poor health, several authors make policy recommendations that are implicitly based on a causal relationship. For example, Kawachi and Kennedy advocate increasing the minimum wage and expanding the Earned Income Tax Credit in an effort to reduce income inequality, and thereby improve health outcomes. In contrast, the contributions in Part II (policy options) are focused less on income inequality and more on a broad range of determinants of health, including individual income and education, individual race and racism, access to quality medical care, and lifestyle factors such as smoking, diet and exercise. The authors contributing to Part II tend to remain agnostic about the causal effect of income inequality on health, and for good reason. As Newman writes, ‘establishing a direct relationship between inequality and disease mechanisms is a daunting task for which the basic science is still relatively incomplete’ (p. 116). Later in Part III of the volume, Len M Nichols expresses several methodological concerns about the research discussed in the first part of the volume, and asserts his view that ‘the effect of income inequality on health—as opposed to the effect of individual SES on health—has yet to be established’ (p. 134).

The confusion created for the reader by these contrasting viewpoints could have been mitigated by including in-depth research from the opposing camp among the papers in Part I. It is noted by Kawachi and Kennedy, Nichols, and William M Rodgers III that several such papers (admittedly our own) existed at the time of the conference. The volume could have benefited from some discussion of the methodological differences that are responsible for producing such disparate results, and conclusions. This is particularly unfortunate, since the most recent published work in this area is not supportive of a causal relationship between income inequality and health.1–4 Consequently, readers of this volume will be ill-prepared to understand why so many public health researchers now doubt that there is any causal link from inequality to health.

There are several other inconsistencies present in the volume. For example, there are contradictory views about the importance of medical care. Several authors relegate the contribution of medical care to the back-burner (for example, see chapters by S Leonard Syme and Clyde Hertzman), while others stress the importance of policies improving access to and quality of medical care (for example, see chapters by Williams and Nicole Lurie). There is also a difference of opinion on whether the effect of SES on health is causal, or driven by a third factor. Hertzman writes that ‘the gradient (between income and health) can not be explained by reverse causation or differential mobility’ (p. 46), while others leave open the possibility that lifestyle factors and other characteristics are correlated with both income and health, thus creating the appearance of causality (this point is made by both Adler and Nichols). Finally, there is a frustrating contradiction on the question of whether research studies have ever proven that re-distributive social policies (namely Social Security) lead to improvements in health (p. 108 and p. 139).

There is nothing inherently wrong with a collection of conflicting studies, particularly if the editors seize the opportunity to explicate and adjudicate these differences. However in this case, the reader is confronted with policy proposals presented in the introduction and through various statements in the conclusion that are not representative of the views expressed by several of the contributors in their own chapters. This raises many questions for the reader—several of which we have detailed above. In addition to these, there is the question of how the editors compiled the policy recommendations that they delineate in the introduction. For example, at least three contributors (Rodgers, Newman, and Nichols) indicate that additional research should be the highest priority among these policy recommendations, not the lowest, as is presented by the editors.

In summary, this collection does not provide readers with a sufficient introduction to the scientific findings on the relationships between income inequality, SES and health. Consequently, we invite readers interested in continuing their self-guided tour of the literature to peruse one of several recent reviews of the income inequality and health literature.5–7 Further, readers may want to consult recent work on the causal links from SES to health.8,9 Finally, more discussion on the extent and causes of racial disparities in health can be found in Fiscella, Franks, Gold and Clancy10 and a special 2000 issue of the journal Medical Care Research and Review.

References

1 Blakely TA, Lochner K, Kawachi I. Metropolitan area income inequality and self-rated health—a multi-level study. Soc Sci Med 2002;54:65–77.[CrossRef][ISI][Medline]

2 Mellor JM, Milyo J. Re-examining the ecological association between income inequality and health. Journal of Health Politics, Policy and Law 2001a;26:487–522.[ISI][Medline]

3 Mellor JM, Milyo J. Income inequality and individual health: evidence from the Current Population Survey. Journal of Human Resources 2002, Forthcoming.

4 Sturm R, Gresenz CR. Relations of income inequality and family income to chronic medical conditions and mental health disorders: national survey. BMJ 2002;324:20–24.[Abstract/Free Full Text]

5 Mellor JM, Milyo J. Income inequality and health. Journal of Policy Analysis and Management 2001b;20:151–55.[CrossRef][ISI][Medline]

6 Milyo J, Mellor JM. Is inequality bad for our health? Critical Review 1999;13(3/4):359–72.

7 Wagstaff A, van Doorslaer E. Income inequality and health: what does the literature tell us? Annu Rev Public Health 2000;21:543–67.[CrossRef][ISI][Medline]

8 Meara E. Why is health related to socioeconomic status? The case of pregnancy and low birth weight. Cambridge MA: National Bureau of Economic Research Working Paper Series, Number 8231, April 2001. Available on-line at http://papers.nber.org/papers/w8231

9 Smith JP. Healthy bodies and thick wallets: the dual relation between health and economic status. Journal of Economic Perspectives 1999; 13:145–66.[ISI]

10 Fiscella K, Franks P, Gold MR, Clancy CM. Inequality in quality: addressing socioeconomic, racial and ethnic disparities in health care. JAMA 2000;283:2579–84.[Abstract/Free Full Text]





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