Editing Gini coefficient (section)

=== Income mobility ===
In 1978, [[Anthony Shorrocks]] introduced a measure based on income Gini coefficients to estimate income mobility.<ref>{{Cite journal | last = Shorrocks | first = Anthony | title = Income inequality and income mobility | journal = Journal of Economic Theory | volume = 19 | issue = 2 | pages = 376–393 | doi = 10.1016/0022-0531(78)90101-1 | date = December 1978 }}</ref> This measure, generalized by Maasoumi and Zandvakili,<ref>{{cite journal|first1=Esfandiar|last1=Maasoumi|first2=Sourushe|last2=Zandvakili| year=1986|title=A class of generalized measures of mobility with applications|journal=Economics Letters|volume= 22|issue=1|pages= 97–102|doi=10.1016/0165-1765(86)90150-3}}</ref> is now generally referred to as [[Shorrocks index]], sometimes as Shorrocks mobility index or Shorrocks rigidity index. It attempts to estimate whether the income inequality Gini coefficient is permanent or temporary and to what extent a country or region enables economic mobility to its people so that they can move from one (e.g., bottom 20%) income quantile to another (e.g., middle 20%) over time. In other words, the Shorrocks index compares inequality of short-term earnings, such as the annual income of households, to inequality of long-term earnings, such as 5-year or 10-year total income for the same households.

Shorrocks index is calculated in several different ways, a common approach being from the ratio of income Gini coefficients between short-term and long-term for the same region or country.<ref name=kss2010>{{cite journal|title=Earnings Inequality and Mobility in the United States: Evidence from Social Security Data Since 1937|first1=Wojciech|last1=Kopczuk |first2=Emmanuel|last2=Saez |first3=Jae|last3=Song |journal=The Quarterly Journal of Economics|year=2010|volume= 125|issue=1|pages= 91–128|doi=10.1162/qjec.2010.125.1.91|jstor=40506278|url=http://emlab.berkeley.edu/~saez/kopczuk-saez-songQJE09SSA.pdf |archive-url=https://web.archive.org/web/20130513122750/http://emlab.berkeley.edu/~saez/kopczuk-saez-songQJE09SSA.pdf |archive-date=2013-05-13 |url-status=live}}</ref>

A 2010 study using social security income data for the United States since 1937 and Gini-based Shorrock's indices concludes that income mobility in the United States has had a complicated history, primarily due to the mass influx of women into the American labor force after World War II. Income inequality and income mobility trends have been different for men and women workers between 1937 and the 2000s. When men and women are considered together, the Gini coefficient-based Shorrocks index trends imply long-term income inequality has been substantially reduced among all workers, in recent decades for the United States.<ref name=kss2010 /> Other scholars, using just 1990s data or other short periods have come to different conclusions.<ref>{{cite journal|title=Cross-national Differences in Income Mobility: Evidence from Canada, the United States, Great Britain and Germany |first=Wen-Hao|last=Chen|s2cid=62886186|journal=Review of Income and Wealth|volume=55|issue=1|pages=75–100|date= March 2009|doi=10.1111/j.1475-4991.2008.00307.x}}</ref> For example, Sastre and Ayala conclude from their study of income Gini coefficient data between 1993 and 1998 for six developed economies that France had the least income mobility, Italy the highest, and the United States and Germany intermediate levels of income mobility over those five years.<ref>{{cite web|title=Europe vs. The United States: Is There a Trade-Off Between Mobility and Inequality?|first1=Mercedes|last1=Sastre|first2=Luis|last2=Ayala |publisher=Institute for Social and Economic Research, University of Essex|url=http://www.ucm.es/info/econeuro/documentos/documentos/dt192002.pdf |archive-url=https://web.archive.org/web/20060612200520/http://www.ucm.es/info/econeuro/documentos/documentos/dt192002.pdf |archive-date=2006-06-12 |url-status=live|year=2002}}</ref>