On the choice of absolute or relative inequality measures.

CONTEXT: In a recent article in this journal, Sam Harper and his colleagues (2010) call for increased awareness and open dialogue of moral judgments underlying health inequality measures. They recommend that analysts use relative inequality measures when concerned only about health inequality but use absolute inequality measures when also concerned about other issues, such as the overall level of population health and the level of health for each group in the population.
METHODS: Using a simple, hypothetical example, this commentary shows that the relationships among inequality, the absolute level for each group, and the overall level in the population are more complex than suggested by the analysis by Harper and his colleagues.
FINDINGS: First, analysts must make the choice of absolute or relative inequality measures, separately, for single- and multiple-population cases. Second, in the single-population cases, analysts can use both relative and absolute inequality measures when concerned only about health inequality independent of other considerations. Third, in almost all real-world multiple-population cases, when using either the absolute or relative inequality measure, the assessment of health inequality is influenced by the absolute level of health for each group.
CONCLUSIONS: The choice between absolute and relative inequality measures is not about the independent normative significance of inequality, as Harper and his colleagues suggest. In choosing between absolute and relative measures, future work needs to integrate an empirical examination of values, a moral assessment of values, and a technical understanding of inequality measures.