How do voter lists get built and kept up to date, and why do names go wrong?

A voter list is built from official records, kept current by checking those records against each other, and it goes wrong mostly when two different people look the same on paper. Voter registration means a person who is eligible to vote must be listed on an electoral roll, which is usually a prerequisite for being allowed to vote.

Countries build the list in different ways. In some places registration is automatic, drawn from government records. In Belgium, for instance, each municipality compiles its voter list from a continuously updated National Register and automatically sends each voter an invitation card. In others, eligible voters have to apply, and update their details when they move. The UK lets electors register with a local authority at any time of the year, replacing an older twice-yearly census that often left out people who had moved.

Keeping the list current is a second job. The US National Voter Registration Act of 1993 requires states to keep lists accurate by identifying people who have died or moved away, but with safeguards, such as no removal programs within 90 days of a federal election. States also check lists against each other, which is where names can go wrong.

One program, Interstate Voter Registration Crosscheck, compared voter rolls from many states looking for people registered twice, matching on first name, last name and full date of birth. In 2017 it examined 98 million records from 28 states and sent back 7.2 million "potential duplicate registrant" records. Independent researchers pointed to Virginia's own 2013 list maintenance report, which documented a 75% false positive rate. In Ada County, Idaho, officials relying on the list mistakenly removed 766 voters, and none were duplicate registrants.

The lesson is not that checking lists is wrong. It is that a matching rule that sounds precise can flag many different people who just happen to share a name and a birthday.