Compare methods

	Index of Dissimilarity	Palma Ratio
Field	Sociology	Sociology
Family	Process / pipeline	Process / pipeline
Year of origin	1955	2011 (Palma's finding); 2013–2014 (the ratio)
Originator	Otis Dudley Duncan & Beverly Duncan	Gabriel Palma; named by Cobham & Sumner
Type	Index of evenness of two groups across units	Tail-ratio inequality measure
Seminal source	Duncan, O. D., & Duncan, B. (1955). A methodological analysis of segregation indexes. American Sociological Review, 20(2), 210–217.	Cobham, A., & Sumner, A. (2014). Is inequality all about the tails? The Palma measure of income inequality. Significance, 11(1), 10–13.
Aliases	dissimilarity index, Duncan index, D index, segregation index	Palma index, Palma measure, top10/bottom40 ratio
Related	5	5
Summary	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.	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.