The Current Population Survey’s Voting and Registration Supplement is the gold standard to understand voter turnout in the United States.  The study is the largest ongoing survey of voting participation in the United States, and is used not only by political scientists, election lawyers and civil rights advocates, but is also cited by Supreme Court Justices.

Michael McDonald  of the United States Election project has been warning for years that CPS turnout estimates were beginning to deviate in worrisome ways from data collected from exit polls, validated surveys, and official election returns.

New research in the Public Opinion Quarterly by Aram Hur and Christopher Achen validates McDonald’s claims.

From the abstract:

The Voting and Registration Supplement to the Current Population Survey (CPS) employs a large sample size and has a very high response rate, and thus is often regarded as the gold standard among turnout surveys. In 2008, however, the CPS inaccurately estimated that presidential turnout had undergone a small decrease from 2004. We show that growing nonresponse plus a long-standing but idiosyncratic Census coding decision was responsible. We suggest that to cope with nonresponse and overreporting, users of the Voting Supplement sample should weight it to reflect actual state vote counts.

Important reading for anyone who uses the CPS.