GUEST EDITORIAL Can We Actually Measure Health Disparities ?

F several decades, researchers around the world have studied demographic disparities in mortality. It is hard to know exactly how much money has been spent on this research. But certainly the amounts have run into the hundreds of million dollars. And, by and large, the conclusions of that research have been the same: The disparities have been increasing. But what if all that research was simply wrong, or, at best, confused to the point of offering negligible insight into the dynamics of group differences in experiencing adverse and favorable health outcomes? I explain below why this is pretty much the case and then address whether there is a better way to do it. The main problem with existing research lies in the failure to recognize the following statistical tendency, which we’ll call heuristic rule X (HRX): When two groups differ in their susceptibility to an outcome, the rarer the outcome, the greater the disparity in experiencing the outcome and the smaller the disparity in avoiding the outcome. Readily available income data illustrate HRX. The U.S. Census Bureau provides data on the number and proportion of each race falling below various percentages of the poverty line. Table 1 presents key elements of that data for blacks and whites in 2004, along with a number of fields expressing statistical relationships stemming from those elements. The information in Table 1 underlies the figures that follow and many of the points in the text. It should be recognized, however, that the essential aspects of the relationships reflected in the table and described below would be found in any set of data reflecting more or less normal distributions of factors associated with whether one experiences or avoids some outcome. Figure 1, which shows the proportions of blacks and whites falling below each of the percentages of the poverty line, provides what may be the best visual illustration of crucial aspects of the data. Consider what these data show for blacks and whites with respect to poverty. Blacks are more likely to be poor than whites, and, as is generally the case when one group is more susceptible to an outcome than another, blacks comprise a larger proportion of each segment of the combined black and white population that is increasingly susceptible to poverty. Correspondingly, the ratio of the black rate to the white rate of falling below each income level increases as the income level declines. For example, the black rate of falling below the poverty line (24.7%) is 2.3 times the white rate (10.8 %). But the black rate of the rarer event of falling below 50% of the poverty line (11.7%) is 2.7 times the GUEST EDITORIAL