Since 1979, states in the Northeast have recorded the biggest increase in the wealth gap as fewer people control higher amounts of state income, according to a data analysis by The Associated Press.
Income inequality is often measured by the Gini index, named for Italian statistician Corrado Gini, who developed it in 1912. It measures income distribution on a scale of zero to one, with zero meaning everyone has the same income and one indicating that a single person has all the income. The higher the number, the greater the amount of income inequality.
This map and dataset take state-by-state look at the Gini rating measurements by household in 1979 compared with 2012, the latest year for which figures are available from the U.S. Census Bureau. The data includes the the District of Columbia and the United States as a whole.