Voter registration is the backbone of the American electoral system. Registration problems create barriers to voting and make it difficult for administrators to communicate with voters, identify voters at the polls, and audit elections after the fact. Reforms following the 2000 election sought to improve the accuracy and currency of the voter-registration lists. Most important, all states now have statewide voter files. So how good are the files today?

This summer the Institute for Quantitative Social Sciences at Harvard University and the Caltech/MIT Voting Technology Project issued the first comprehensive, nationwide analysis of the quality of information stored on voter registration lists.

The graph below shows the results. Based on data compiled by Catalist—a political-data vendor that supports Democrat-leaning organizations but has effectively compiled a national voter registration database without partisan influence—the figure depicts the proportion of registration records that are “unmailable.” Either the registrant has moved or died, or the listed address is invalid.

Nationwide, approximately 1 in 16 entries on the registration lists is unmailable. The magnitude of the problem varies greatly throughout the country. In California, Massachusetts, and Washington, D.C., about 1 in 50 entries is problematic, but in Arkansas, that number is 1 in 5.