Invited commentary: measuring social disparities in health--what was the question again?

Monitoring social disparities in health is not a straightforward project. Defining what constitutes a disparity is challenging, and multiple measures have been proposed to track changes in disparity over time. In this issue, Harper et al. (Am J Epidemiol 2008;167:889-899) present seven health disparity measures and apply them to US lung cancer incidence rates (1992-2004). They find that different summary measures provide different answers to the question "Has disparity increased or decreased?" Their findings leave us uncertain how to use and interpret these measures to track changes in social disparities in health. In this invited commentary, the author proposes that increased attention to the scale at which disparities are measured, the interpretations attached to the various measures used, and the way in which these measures are assembled on the basis of conceptual models would benefit the field. Specifically, attention to these three areas would increase the capacity to communicate research findings to the public and policy-making consumers of disparity-related research.