Regional Income Inequality in the United States (1917-2011)

Estelle Sommeiller is a socio-economist at the Institute for Research in Economic and Social Sciences (IRES) in France. She holds a Ph.D. in economics, jointly awarded by the University of Delaware and the Université Lumière in Lyon, France. Her doctoral dissertation, "Regional Inequality in the United States, 1913-2003", analyses a set of panel data by state cross-sections and annually, using the Statistics of Income publications by the US Internal Revenue Service (IRS). Sommeiller's theoretical approach was inspired by the economist Thomas Piketty, who pointed out the strong heterogeneity of the top decile in his book "Les hauts revenus en France au XXème siècle. Inégalités et redistributions 1901-1998." and distinguished a certain number of intermediary revenues classes (the fractiles), until the highest 0.01. The same distinction was used by Sommelier, with the use of the desegregation by state as a difference. Two variables were extracted by the author from the publications of the IRS: the number of individual returns and the total income expressed in dollars. Both variables are ranked by size of income and by state. The database represents well the top 10 percent of the income distribution. Sommeiller's Ph.D. thesis covers the period from 1913 to 2003 with deflated measures, using the 2003 dollars value. For the purposes of the paper "The Increasingly Unequal States of America", Sommeiller updated the data by adding the 2004 to 2011 series and excluding the ones from 1913 to 1916. All the measures are expressed in 2011 current dollars. These are the data that we are disseminating here.