Author: Michael Herndon, Ph.D. | Senior Research Fellow, UCLA Voting Rights Project | September 2026

Evidence from California and Washington shows that non-White voters are disproportionately more likely to have their vote-by-mail ballots rejected – and that this problem may be rooted in the racial biases of election officials, rather than voter deficiencies.

THE BOTTOM LINE

• Vote-by-mail (VBM) now accounts for over a third of ballots cast nationally, and in California, 89 percent of voters cast their ballots this way.
• Signature verification is the single largest source of ballot rejection. In California and Washington, non-matching signatures accounted for 59 and 64 percent of all rejected ballots in the 2024 general election respectively.
• Non-White voters are disproportionately affected. Studies using real election data from California and Washington find that non-White voters and young voters are significantly more likely to have their ballots rejected for signature discrepancies, late arriving ballots, and undeliverable ballots.
• Personal biases can affect signature adjudication. Controlled experiments suggest that the average person is more likely to be accepting of White appearing signatures than non-White appearing signatures, even when controlling for signature quality, complexity, etc. Participants in these experiments were also observed to be influenced by their personal racial beliefs.
• Closing these demographic gaps in ballot rejection requires scientifically backed administrative reforms. To this end, more research is needed on the effectiveness of different technologies, training materials, workflows, etc. on making ballot rejection more precise and less biased.

THE PROBLEM

Vote-by-mail was designed to make voting easier, and for most voters it does. But every general election, more than 500,000 mail ballots are rejected nationwide — and research suggests that at minimum 80 percent of these ballots belong to eligible voters.This matters because in close elections, wrongly rejected ballots can make the difference between winning and losing. For example, in 2024, California’s 13th Congressional District was decided by just 187 votes, in a race where more than 6,000 ballots were flagged for missing or non-matching signatures.The 2004 Washington gubernatorial election was decided by just 129 votes while simultaneously rejecting thousands of VBM ballots. Hundreds of state and local elections are decided by similarly thin margins every cycle, reminding us of the power and impact that even a single wrongfully rejected ballot can have.

The most common reason ballots are rejected is a signature mismatch: an election worker’s judgment call that the signature on a ballot envelope doesn’t sufficiently resemble the signature on file. Unlike a missed deadline, signature verification is a subjective determination made in seconds, often with only minimal training compared to the 2 years required to be a certified forensic document examiner. Meanwhile, election skepticism is alarmingly high – especially among Republicans.

Continue reading How Racial Biases Can Affect Vote-by-Mail Ballot Rejection