Based on the Gini index, income inequality increased by 1.6 percent between 2010 and 2011; this represents the first time the Gini index has shown an annual increase since 1993, the earliest year available for comparable measures of income inequality. The Gini index was 0.477 in 2011. (The Gini index is a measure of household income inequality; zero represents perfect income equality and 1 perfect inequality.)
Income inequality also increased between 2010 and 2011 when measured by shares of aggregate household income received by quintiles. The aggregate share of income declined for the middle and fourth quintiles. The share of aggregate income increased 1.6 percent for the highest quintile and within the highest quintile, the share of aggregate income for the top 5 percent increased 4.9 percent. The changes in the shares of aggregate income for the lowest two quintiles were not statistically significant.
In 2011, 13.7 percent of people 18 to 64 (26.5 million) were in poverty compared with 8.7 percent of people 65 and older (3.6 million) and 21.9 percent of children under 18.