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	Palma Ratio	Atkinson Index	Index of Dissimilarity
Field	Sociology	Sociology	Sociology
Family	Process / pipeline	Process / pipeline	Process / pipeline
Year of origin	2011 (Palma's finding); 2013–2014 (the ratio)	1970	1955
Originator	Gabriel Palma; named by Cobham & Sumner	Anthony Barnes Atkinson	Otis Dudley Duncan & Beverly Duncan
Type	Tail-ratio inequality measure	Welfare-based, parameterized inequality index	Index of evenness of two groups across units
Seminal source	Cobham, A., & Sumner, A. (2014). Is inequality all about the tails? The Palma measure of income inequality. Significance, 11(1), 10–13.	Atkinson, A. B. (1970). On the measurement of inequality. Journal of Economic Theory, 2(3), 244–263.	Duncan, O. D., & Duncan, B. (1955). A methodological analysis of segregation indexes. American Sociological Review, 20(2), 210–217.
Aliases	Palma index, Palma measure, top10/bottom40 ratio	Atkinson inequality measure, Atkinson's A, welfare-based inequality index	dissimilarity index, Duncan index, D index, segregation index
Related	5	5	5
Summary	The Palma ratio measures income inequality as the ratio of the income share held by the richest 10 percent of the population to the share held by the poorest 40 percent. It rests on the empirical regularity, documented by Gabriel Palma, that the middle deciles (5 through 9) capture a remarkably stable half of national income across countries, so that inequality is essentially a contest between the top and the bottom — the 'tails' of the distribution.	The Atkinson index is a welfare-based measure of inequality that incorporates an explicit, analyst-chosen parameter for how much society dislikes inequality. Introduced by Anthony Atkinson in 1970, it asks what fraction of total income could be discarded, under an equal distribution, while leaving social welfare unchanged — making the ethical judgement behind any inequality comparison transparent rather than hidden.	The index of dissimilarity, often called the Duncan segregation index, measures how unevenly two groups — such as two racial or occupational groups — are distributed across a set of units like neighborhoods, schools, or occupations. It ranges from 0, when both groups have identical distributions across units, to 1, when the units are completely segregated, and has the intuitive interpretation of the share of one group that would have to relocate to achieve an even distribution.