Caltech Science Exchange / Topics / Voting and Elections / Voting by Mail

How Does Voting by Mail Work?

The COVID-19 pandemic prompted a number of states to expand access to mail-in ballots. While in previous American elections, most voters have cast their ballots in person, mail-in voting has a long history in the United States. The practice dates back to the Civil War, when soldiers were given the opportunity to vote from the battlefield.

A small but growing number of states deliver mail-in ballots to all registered voters. All states, along with Washington D.C., offer the option of voting by mail, though some require voters to provide a valid reason why they cannot vote in person.

A quirk in California's law created a natural experiment that shed light on the impact of universal vote-by-mail on voter turnout. Caltech professor of political and computational social science Michael Alvarez explains in this video.

What about fraud?

A 2020 report from the University of New Mexico's Center for Social Policy, the UCLA Voting Rights Project, and the Union of Concerned Scientists concluded that incidents of mail-in ballot fraud are rare, including in states that have adopted universal vote-by-mail systems. For example, an analysis of 2016 election data in Oregon identified 10 instances of fraudulent ballots out of 2 million votes cast.

Similarly, researchers at Caltech have agreed that while mail-in ballots may be more vulnerable to fraud or tampering than ballots cast in person, security measures minimize those risks.

What about lost votes?

While fraud associated with mail-in voting is negligible, the potential for so-called lost votes may be more significant.

A "lost vote" is not necessarily physically lost. Instead, the term refers to a vote an individual intended to cast, but that was not ultimately counted. Votes may be lost because a ballot was received too late, for example, or because of voter error, including overvotes (when a voter makes more selections than allowed in a given contest) and undervotes (when a voter skips a contest altogether).

Charles Stewart III, Co-Director of the Caltech/MIT Voting Technology Project, has noted that there is potential for votes to be lost at all stages of the vote-by-mail pipeline, which often includes:

The voter's request for a mail-in ballot
Verification of the mail-in ballot request
Delivery of the ballot
Completion of the ballot
Return of the ballot
Verification of the ballot
Tabulation of the ballot

Securing mail-in ballots

Election officials have implemented a number of safeguards to protect the mail-in voting process. These include identity and signature verification, bar codes on ballot envelopes that allow voters to know whether their ballot has been received, ballot tracking through the U.S. Postal Service, and post-election audits, among other measures.

In addition, some states have made it illegal for volunteers or workers to gather and submit mail-in ballots, a practice known as "ballot collecting," because of the potential for fraud, coercion, or vote manipulation.

Ballot design represents yet another safety measure. The production of counterfeit ballots would require mimicking a ballot's size, style, paper weight, envelope, and other features, which differ by county and often change with every election cycle. Each counterfeit ballot would then have to match the name and signature of a registered voter in order to be counted.

What's the difference between absentee voting and vote-by-mail?

Absentee voting allows a person to request a ballot in the mail, and in some states justification is required. In states that have adopted "vote-by-mail" processes, a ballot is sent to every registered voter without the need for a request.

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