Compare methods

	Atkinson Index	Palma Ratio
Field	Sociology	Sociology
Family	Process / pipeline	Process / pipeline
Year of origin	1970	2011 (Palma's finding); 2013–2014 (the ratio)
Originator	Anthony Barnes Atkinson	Gabriel Palma; named by Cobham & Sumner
Type	Welfare-based, parameterized inequality index	Tail-ratio inequality measure
Seminal source	Atkinson, A. B. (1970). On the measurement of inequality. Journal of Economic Theory, 2(3), 244–263.	Cobham, A., & Sumner, A. (2014). Is inequality all about the tails? The Palma measure of income inequality. Significance, 11(1), 10–13.
Aliases	Atkinson inequality measure, Atkinson's A, welfare-based inequality index	Palma index, Palma measure, top10/bottom40 ratio
Related	5	5
Summary	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 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.