The chart below, based on Census data analyzed by the liberal think tank Demos, illustrates the relationship between income and voter turnout.
The data, which uses the 2008 election as a benchmark, finds that voter turnout is roughly flat at 41 percent for those who make under $15,000 per year. After that, turnout rises in every subsequent income bracket, peaking at 78 percent among Americans who earn $150,000 or more.
The Demos paper is called "Stacked Deck: How the Dominance of Politics by the Affluent & Business Undermines Economic Mobility in America." It is available here.