According to the the latest American Community Survey data, the period from 2007 to 2014 saw a statistically significant increase in income inequality – represented by the Gini index – in 32 states. The Gini Index represents the concentration of income in a given state or country, in a range from 0 to 1. A higher Gini index indicates greater inequality – where income is concentrated among a relatively few individuals or households; a lower Gini score represents more even income distribution.
The ACS 1-Year reports the Gini index for households in table B19083 as the middle point of a 90% confidence interval, along with a corresponding margin of error. The visualization below calculates significant change in Gini index scores from 2007-2014 – shifts outside the margin of error. In 32 states, the lower end of the range of the 2014 Gini estimate was greater than the upper range of the 2009 Gini Index estimate. In the remaining states, there was no statistically significant change from 2009 to 2014: in these cases, taking into account the margin of error, the estimates from 2009 overlapped with those from 2014.