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	Concentration Curve and Index	Concentration Index	Gini Coefficient	Lorenz Curve
Field	Economics	Social Epidemiology	Sociology	Sociology
Family	Process / pipeline	Process / pipeline	Process / pipeline	Process / pipeline
Year of origin	1991	1991	1912	1905
Originator	Adam Wagstaff, Pierella Paci & Eddy van Doorslaer	Adam Wagstaff, Pierfilippo Paci & Eddy van Doorslaer; Nanak Kakwani	Corrado Gini	Max Otto Lorenz
Type	Bivariate inequality measure	Rank-based summary index of socioeconomic inequality in health	Scalar measure of statistical dispersion / inequality	Graphical representation of distributional inequality
Seminal source	Wagstaff, A., Paci, P., & van Doorslaer, E. (1991). On the measurement of inequalities in health. Social Science & Medicine, 33(5), 545–557.	Wagstaff, A., Paci, P., & van Doorslaer, E. (1991). On the measurement of inequalities in health. Social Science & Medicine, 33(5), 545-557.	Ceriani, L., & Verme, P. (2012). The origins of the Gini index: extracts from Variabilità e Mutabilità (1912) by Corrado Gini. The Journal of Economic Inequality, 10(3), 421–443.	Lorenz, M. O. (1905). Methods of measuring the concentration of wealth. Publications of the American Statistical Association, 9(70), 209–219.
Aliases	Health Concentration Index, Concentration Curve, Socioeconomic Inequality in Health Index, Wagstaff Index	Health Concentration Index, Concentration Curve and Index, Wagstaff Concentration Index, Erreygers Corrected Concentration Index	Gini index, Gini ratio, Gini concentration ratio, G	Lorenz concentration curve, Lorenz diagram, cumulative share curve
Related	3	4	5	5
Summary	The concentration curve and concentration index, established as the standard tools for measuring socioeconomic inequality in health by Wagstaff, Paci, and van Doorslaer in 1991, capture how a health variable is distributed across the population ranked by socioeconomic status. The concentration curve plots the cumulative share of health (or ill-health) against the cumulative share of people ordered from poorest to richest; the concentration index is twice the area between this curve and the line of equality. Unlike the Gini coefficient, which measures pure dispersion, the concentration index is bivariate — it measures inequality in one variable that is systematically related to a second, socioeconomic ranking.	The concentration index is the standard summary measure of socioeconomic inequality in health: it quantifies the degree to which a health outcome - illness, mortality, malnutrition, or healthcare use - is disproportionately concentrated among the poor or the rich. It is built from the concentration curve, which plots the cumulative share of health against the cumulative share of the population ranked from poorest to richest, and the index is simply twice the area between that curve and the line of perfect equality. Wagstaff, Paci, and van Doorslaer's 1991 critique of inequality measures argued that, unlike the simple range or the Gini, the concentration index properly reflects the socioeconomic dimension of health inequality and the experience of the whole distribution. Kakwani, Wagstaff, and van Doorslaer's 1997 paper then supplied a computational formula, a convenient regression estimator, and the asymptotic variance needed for statistical inference. The index ranges from minus one to plus one, with zero meaning no socioeconomic gradient, a negative value meaning ill health concentrates among the poor, and a positive value the reverse. It has become the lingua franca of health-equity monitoring at agencies like the World Bank and WHO.	The Gini coefficient is the most widely used single-number summary of inequality in a distribution such as income or wealth. Introduced by the Italian statistician Corrado Gini in 1912, it equals twice the area between the Lorenz curve and the line of perfect equality, ranging from 0 when everyone has the same amount to a maximum approaching 1 when one unit holds everything.	The Lorenz curve is a graphical device that displays the full shape of inequality in a distribution by plotting the cumulative share of a quantity (such as income) held by the cumulative share of the population, ranked from poorest to richest. Introduced by Max Lorenz in 1905, it underlies the Gini coefficient and provides the basis for ranking distributions by inequality when one curve lies entirely above another.