We can identify three commonly used definitions of racial/ethnic health care disparities, each associated with corresponding statistical methods (). The first focuses on the race/ethnicity coefficient in a multivariate regression model after adjustment for all other factors available to the researcher, including socioeconomic status (SES) variables; we call this estimator the “residual direct effect” (RDE). This definition makes no distinction between variables which may be legitimate sources of differences in utilization (e.g., health status) and those which may represent race-related disadvantage whose effects on utilization are of concern (e.g., education, income, and other measures of SES). Controlling for the latter tends to “absorb” some of the effect of race/ethnicity, so the RDE estimates only that part of racial differences not mediated through measurable disadvantage.
Summary of Three Main Definitions and Methods of Disparities Measurement with Examples, Pros, and Cons
Another definition is exemplified in both Healthy People 2010
) and the AHRQ National Healthcare Disparities Reports (NHDR) (AHRQ 2004
, p. 7): “In pursuit of the overarching goal of eliminating health disparities, all differences among populations in measures of health and health care are considered evidence of disparities.” This definition is implemented by simply assessing differences in group means. A limitation of this definition is that racial/ethnic group differences that many would consider to be appropriate in an equitable health care system because of intergroup differences in need (e.g., as being due to differences in distributions of age or health status) are included in these differences in utilization.
We prefer a third definition of racial/ethnic health care disparity based on the definition put forth in the Unequal Treatment report
): disparities are differences in health care services received by the two groups that are not due to differences in the underlying health care needs or preferences of members of the groups.2
Differences that are considered to be disparities include differences due to the operation of health care systems, the legal and regulatory climate, discrimination, or other factors (). We focus here on the IOM definition because (1) we believe it correctly parses out the differences that are just and unjust, and (2) implementation of the IOM definition requires statistical methods that are not as familiar to the health services research field as methods of implementing the major alternative definitions.
Figure 1 The Institute of Medicine (IOM 2003, p. 4) Definition of Racial/Ethnic Healthcare Disparities
An important contribution of the IOM definition is that it explicitly specifies the sources of racial/ethnic health care differences, distinguishing which should be considered to contribute to a disparity. Exclusion of differences due to clinical need and appropriateness (assessed by health status variables) from disparities reflects the normative stance that these differences are allowable. For example, in some analyses we found the Latino group to be healthier than non-Hispanic whites (younger on average and with lower rates of illness based on available diagnostic variables) and therefore to have a clinically predictable lesser need for care (Cook, McGuire, and Zuvekas 2009a
; Cook et al. 2010
). The health care system should therefore not be faulted for providing them with less care commensurate with their predicted difference in needs. On the other hand, in many analyses blacks have more severe illness than a white comparison group. In this case, a health care system that provides the same amount of services to blacks as whites would be providing disparate care according to the IOM definition given the greater clinical needs of the black population. In these examples, adjustment of health status operates differently for the two populations. Adjusting for health status and age, the Latino use would move from lower use than whites to zero difference, whereas black use would move from zero difference to lower use than whites.
The IOM definition includes as part of the disparity differences that are due to SES and other individual characteristics other than health status, reflecting a view that differences in care provided due to SES factors such as income and education are unjustifiable and health systems should be accountable for such differences. In many of our prior studies, we have found both Latinos and blacks to have lower SES characteristics than whites and that the lower SES groups receive less treatment than whites. These differences are not warranted and should contribute to the disparity according to the IOM.
The introduction of the IOM definition of health care disparities into the racial/ethnic health care disparities literature has been criticized on two grounds. The first is that the IOM definition does not isolate “racial” disparities. According to this critique, differences due to socioeconomic factors should not be included in the disparity calculation, so the residual race effect (i.e., the RDE from above), after adjustment for these factors, should be the measure of disparity (Klick and Satel 2006
). Like Bloche (2004)
, we counter that health care systems should not be providing poorer treatment to individuals in lower SES categories, and hence mediation of racial/ethnic differences by income, wealth, insurance, and other socioeconomic factors does not negate racial/ethnic disparities. Rather, identification of SES as a mediator is policy relevant and may help to identify approaches to ameliorate the racial/ethnic disparities.
The second critique conversely objects to adjustment for health status in the IOM definition because differences in health status have systematic historical and structural causes that should be addressed. We counter that our analyses are intended to measure the current performance of health care systems for the population. The equity of health care systems should be evaluated by a definition that tracks their performance with clinically comparable groups of patients of different races/ethnicities, unaffected by differences in the current case mix of patients due to factors not controlled by the system under evaluation.
The debate on the correct definition of racial/ethnic health care disparity not only has a significant impact on disparities measurement and results but also is of policy significance given the large number of private and government institutions funding initiatives and research on reducing disparities. Implementing a consistent definition with suitable methods is key to establishing baseline rates of health care use and quality, tracking disparities, and evaluating policy and systems interventions.