Wagstaff et al. (1991) proposed to use the related concepts of a concentration curve and index
to measure the extent to which inequalities in health are related to indicators of socioeconomic
status like income or education. They argued that the concentration index meets three minimal
requirements of an inequality index: (i) it reflects the experience of the entire population studied,
(ii) it reflects the socioeconomic dimension of health inequalities and (iii) it is sensitive to changes
in the composition of the underlying socioeconomic ranking variable. A concentration curve
describes the cumulative distribution of health in a population ranked by socioeconomic status
and the concentration index, henceforth denoted as C, measures the deviation from an equal
distribution as (twice) the area between the concentration curve and the diagonal