Background: Racial disparities in the burden of sexually transmitted diseases (STDs) have been documented and described for decades. Similarly, methodological issues and limitations in the use of disparity measures to quantify disparities in health have also been well documented. The purpose of this study was to use historic STD surveillance data to illustrate four of the most well-known methodological issues associated with the use of disparity measures.
Methods: We manually searched STD surveillance reports to find examples of racial/ethnic distributions of reported STDs that illustrate key methodological issues in the use of disparity measures. The disparity measures we calculated included the black-white rate ratio, the Index of Disparity (weighted and unweighted by subgroup population), and the Gini coefficient.
Results: The 4 examples we developed included illustrations of potential differences in relative and absolute disparity measures, potential differences in weighted and nonweighted disparity measures, the importance of the reference point when calculating disparities, and differences in disparity measures in the assessment of trends in disparities over time. For example, the gonorrhea rate increased for all minority groups (relative to whites) from 1992 to 1993, yet the Index of Disparity suggested that racial/ethnic disparities had decreased.
Conclusions: Although imperfect, disparity measures can be useful to quantify racial/ethnic disparities in STDs, to assess trends in these disparities, and to inform interventions to reduce these disparities. Our study uses reported STD rates to illustrate potential methodological issues with these disparity measures and highlights key considerations when selecting disparity measures for quantifying disparities in STDs.