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	Concentration Index	Health Inequality Gini Decomposition
Dziedzina	Social Epidemiology	Social Epidemiology
Rodzina	Process / pipeline	Process / pipeline
Rok powstania	1991	1985
Twórca	Adam Wagstaff, Pierfilippo Paci & Eddy van Doorslaer; Nanak Kakwani	Robert Lerman & Shlomo Yitzhaki; Adam Wagstaff & Eddy van Doorslaer
Typ	Rank-based summary index of socioeconomic inequality in health	Inequality-measurement and decomposition pipeline
Źródło pierwotne	Wagstaff, A., Paci, P., & van Doorslaer, E. (1991). On the measurement of inequalities in health. Social Science & Medicine, 33(5), 545-557.	Lerman, R. I., & Yitzhaki, S. (1985). Income inequality effects by income source: A new approach and applications to the United States. The Review of Economics and Statistics, 67(1), 151-156.
Inne nazwy	Health Concentration Index, Concentration Curve and Index, Wagstaff Concentration Index, Erreygers Corrected Concentration Index	Health Gini Decomposition, Gini Decomposition by Source, Inter-Individual Health Inequality, Total Health Inequality Gini
Pokrewne	4	4
Podsumowanie	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 familiar single-number summary of inequality, and applied to a health variable it captures total, inter-individual health inequality — how unequally health is distributed across all people, regardless of their socioeconomic position. Its real analytic power comes from decomposition. Robert Lerman and Shlomo Yitzhaki's 1985 covariance formulation rewrites the Gini as twice the covariance between health and its rank divided by the mean, which makes it decomposable into the contributions of separate sources or components, each weighted by its share, its own Gini, and its Gini correlation with the overall distribution. The same machinery supports a between-versus-within-group split. As Wagstaff and van Doorslaer's review of health-inequality measurement explains, this 'pure' inequality view complements socioeconomic measures like the concentration index: the Gini asks how unequal health is, while the concentration index asks how that inequality is patterned by income or rank.