Who Votes? Congressional Elections and the American Electorate: 1978–2014

"Voting is among our most fundamental domestic responsibilities and important civic opportunities. Without free and open elections, American democracy would not exist. Maintaining and improving our system of elections requires not only documenting election results, but also understanding the composition of America’s electorate, both historically and presently.
Since 1964, the U.S. Census Bureau has fielded the Voting and Registration Supplement to the Current Population Survey (CPS) every 2 years. Generally speaking, national American elections fall into two categories: elections where voters decide on the office of the President and congressional seats, and elections where congressional seats are the highest offices decided. To avoid confusion with presidential elections, the following report refers to nonpresidential year elections as “congressional elections.” Election results and voting patterns tend to vary between these two types of elections (specifically, voting and registration rates are lower in years with congressional elections only), and the majority of this report will focus on congressional election years only (2014, 2010, 2006, etc.)..."
Voting