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Please excuse my ignorance of economics. I recently learned about the Gini-Coefficient as a measure of the economic inequality in a country. I have since seen several plots of this coefficient over time, each for an individual country. The following is from Equality trust and concerns the UK. United Kingdom, Gini over time

Another plot, concerning various countries, is found here: enter image description here

At first sight, it appears impossible, to construct such a curve for the entire world. Yet, in discussing extreme poverty, I recently learned that incomes can be adjusted to equal purchasing power. Naively it seems, one could measure economic inequality globally. So, are there such data concerning the world as a whole? I know there are maps with countries colour coded by Gini, but this is not what I mean.

My interest is not limited to Gini, if there is another measure, by which the global temporal evolution of inequality can be captured, please tell me!

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    $\begingroup$ You may be able to find relevant information on Thomas Piketty's webpage. The data and charts from Capital in the Twenty-First Century are available there: piketty.pse.ens.fr/en/capital21c2 $\endgroup$ – Winterflags Aug 21 '16 at 8:47
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It is possible, but it involves consiberable work as you need to collect underlying income distributions across the world or to be able to estimate them.

This has been done, for example in a World Bank policy research working paper 6719, Global Income Distribution From the Fall of the Berlin Wall to the Great Recession by Christoph Lakner and Branko Milanovic in December 2013. It included this chart of global income distributions:

Global income distribution

In fact the real story here is the reduction in the number of very-low-income people in absolute terms, especially in countries such as China over 20 years, plus the rise of middle incomes (in a global sense).

It is possible to use this to estimate Gini indices and the paper gives the following estimates:

  • 1988: 72.2
  • 1993: 71.9
  • 1998: 71.5
  • 2003: 71.9
  • 2008: 70.5

Points to take from these numbers are

  • global inequality is wide with a Gini index higher than almost all countries or regions

  • the numbers suggest a global reduction in inequality even when inequality had been increasing within most major countries (especially China)

  • the reduction has been small and can easily reverse (either in the future or on re-estimation of the past)

Regional trends and other inequality measures are in Table 3 of the paper, while other people's estimates of a global Gini index are in the Appendix Table 1.

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