Introduction The purpose of this study was to examine different measures of racial and ethnic disparities in the reported cases of primary and secondary (P&S) syphilis and gonorrhoea from 1981 to 2012 in the United States.
Methods For each year from 1981 to 2012, we calculated values for five disparity measures: the Gini coefficient, two versions of the index of disparity (unweighted and weighted by population subgroup size), the population attributable fraction, and the black-to-white rate ratio. We also examined annual changes in these measures. Specifically, we examined whether or not the five measures yielded consistent assessments as to whether racial and ethnic disparity was increasing or decreasing from one year to the next.
Results Overall, the disparity measures we examined were generally consistent with one another. However, from any given year to the next, the various disparity measures could yield divergent results in terms of whether racial/ethnic disparities in STDs are increasing or decreasing as well as in terms of the relative magnitude of the change. Over the 31-year period, ≥4 of the 5 index measures agreed on the direction of change 28 times for both P&S syphilis and gonorrhoea. The most common measure that had a different direction of change from the other measures was the population attributable fraction.
Conclusion Our findings illustrated two well-known limitations of relative measures of racial/ethnic disparities in health. First, relative measures of disparity can decrease due to increases in STD incidence rates among Non-Hispanic Whites (or increase due to decreases in STD incidence among Non-Hispanic Whites). Second, whether or not racial and ethnic disparities increased from one year to the next can differ across measures of disparity. Reliance on just one measure of disparity can at times lead to divergent conclusions about changes in disparities over short time periods.
Disclosure of interest statement The findings and conclusions in this study are those of the authors and do not necessarily represent the official position of the United States Centres for Disease Control and Prevention (CDC). No external funding was received for this study and the authors have no conflicts of interest.
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