These 3,140 series are calculated from the U.S. Census Bureau’s American Community Survey. For each series, the 20:20 ratio is used to determine the level of inequality in a county. The 20:20 ratio is the ratio of the mean income for the highest quintile (top 20 percent) of earners divided by the mean income of the lowest quintile (bottom 20 percent) of earners for a particular geographical area.