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Ballot Signature Verification & Curing

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Written by Dr. Joshua Mueller
Published on October 31, 2021
Research Highlights

States vary widely in their requirements and protocols for verifying that ballot signatures match signatures in a voter’s registration file. Some states require that voters be notified when their ballot fails the signature verification process so that they may remedy (or “cure”) their ballot.

  • In 2016, 1% of all absentee ballots were rejected nationwide. Signature mismatch was the top reason for ballot rejection (27.5% of all rejections), followed by missed deadlines (23%), missing signature (20%), no witness signature (3%), or problems with return materials (2%).
  • Election officials may use manual or automated signature verification processes.
    • Automated verification is associated with higher signature rejection rates.
  • Inexperienced voters, who tend to be younger voters of color, are more likely to have their ballots rejected due to missing signatures on ballots or return envelopes.
  • Eighteen states, including Iowa and Illinois, require election authorities to notify voters if their signature is rejected and provide an opportunity to fix (“cure”) the problem.
    • Missouri does not require ballot curing.
  • Sending follow-up letters increases the rate of successfully cured ballots.

Executive Summary

Absentee/mail-in and provisional ballots require voters to provide a signature attesting to their identity and eligibility to vote. States vary widely in their requirements and protocols for verifying that ballot signatures match signatures in a voter’s registration file. Some states require that voters be notified when their ballot fails the signature verification process so that they may remedy (or “cure”) their ballot. Ballot curing protocols vary widely between states and localities. Missouri requires local election authorities to design and execute signature verification protocols, but does not require ballot curing.


  • Signature verification and curing protocols vary widely between and within states, and these rules are not always well-documented. As a result, it may be difficult for researchers to assess the effects of these rules on ballot rejection and curing rates.
  • When ballot curing is permitted but not required, protocols are left up to local election authorities, who do not always make their procedures and data publicly available. This can make it difficult to assess how voting outcomes are affected in states without notice and curing requirements.

Research Background

Ballot Signature Verification

Absentee (or “mail-in”) and provisional ballots require one or more voter/witness signatures in order to be counted. When voters in Missouri sign a ballot or the envelope containing their ballot, they are attesting under penalty of perjury to their identity, and that they are eligible to vote. (Mo. Rev. Stat § 115.430, 631, 655)

All states require valid signatures on absentee ballots, and 32 states require signature matching verification to confirm voters’ identities (Figure 1).1 In these cases, county officials verify voter signatures by comparing the signature on the absentee ballot, return envelope, or provisional ballot to the signatures in the voter’s registration file. The ballot is accepted if the signature is considered a match, and either rejected or set aside for further review if the signature does not appear to be a match.2

In general, signature verification protocols are not established by the state; local election authorities are given leeway to design and perform signature verification. In Missouri, judges selected by local election authorities must verify signatures on absentee ballots to voter registration records, but no procedural details are provided in the state statute (Mo. Rev. Stat § 115.655). The U.S. Election Assistance Commission (EAC) provides a short guide to help election administrators manage signature-matching processes. While Missouri does not provide guidance on signature verification, some states (e.g., Colorado, Arizona) provide detailed signature verification guides for their local election authorities.3,4,5

Because signature verification is largely decentralized, signature matching varies greatly between states and counties. For example, some counties use manual signature verification, whereas others use automated (or “algorithmic”) signature matching technology. Evidence from past elections indicates that the use of fully automated signature matching without any human review of ballots may increase the rate of ballot rejections by up to 75%.2 The proportion of “correct/incorrect” rejections by manual and automated systems is unknown, but election officials note that low-resolution digital signatures or illegible signatures from registration files or DMVs may pose difficulties to both types of verification.

Ballot Rejection

The EAC reports that 1% of all absentee ballots were rejected in 2016, and that signature mismatch was the top reason for ballot rejection, accounting for 27.5% of all rejections.6 Other common reasons for rejection include missed deadlines (23%), no voter signature (20%), no witness signature (3%), or problems with return materials (e.g., wrong envelope, ballot missing from envelope; 2%). Election administrators also report a significant number of rejections for reasons categorized as “other reason given”. This categorization is not standardized across counties, so it is unclear what this designation means. It may include improper notarization, incomplete information on a return envelope, or members of a household accidentally signing the wrong return envelopes.7

Inexperienced voters who use absentee ballots are up to 3x more likely to have their ballots rejected compared to experienced mail voters. This likelihood varies by a voter’s party registration, race/ethnicity, and age. Research from the 2018 and 2020 elections in Florida indicates that younger voters and voters of color are more likely to have absentee ballots rejected. This difference in rejection rates is attributed in part to lack of familiarity with voting procedures, which can result in late or improper submission of ballots. For example, younger voters who successfully returned their absentee ballots on time in these elections were disproportionately likely to have omitted their signature on their return envelopes.7

Ballot Curing

As of 2020, 18 states, including Iowa and Illinois, require election authorities to provide notice to voters if their ballot fails the signature verification process (Figure 1). They must also provide the voter with an opportunity to “cure”, or correct, these signature-related issues. Ballot curing eligibility rules vary between states; some allow correction of mismatching or missing signatures, others only allow correction of mismatching (but not missing) signatures. In states that require witness signatures on absentee ballots, such as Wisconsin, voters can cure misplaced or missing witness signatures in addition to their own. Voters may also be able to cure missing Social Security numbers, unsealed envelopes, and problems with ballot statement information. Three states (Missouri, Oklahoma, and Mississippi) require a notary for absentee ballots, but do not allow ballot curing. In response to COVID, five states, including those with Democratic (New Jersey, New York, and Virginia) and split (Michigan, North Carolina) state governments, expanded or enacted a temporary notice and cure policies.1

A curing system requires officials to send voters a letter and blank affidavit describing the reason the voter’s ballot has been rejected and how they remedy the situation. Typically, the voter must mail back the signed affidavit along with a copy of some form of valid identification before a specified deadline. Some states use both a letter and electronic communication to ensure contact with the voter. Once the cured ballot has been received, the ballot receives a second chance to pass the signature verification process. When the signatures match and any necessary identification requirements are met, the ballot can be accepted.6

In addition to variation in ballot curing eligibility between states, there are also differences in deadlines for how quickly officials must contact voters, deadlines for how quickly voters must prove their eligibility, and what methods of verification are acceptable (e.g., mail or electronic communication, identification requirements).

In 2018, California passed the Every Vote Counts Act (EVCA), which requires counties to allow signatures to be remedied by mail, email, and fax. In addition, counties may include return envelopes with pre-paid postage, may request multiple signatures during the remedy process, and may facilitate in-person visits by elections staff to help those with additional needs. Evidence from California in the 2020 election indicates that providing timely follow-up letters (sent only if the first notice is not returned within a week) increases remedy rates; two counties that provided follow-up letters had remedy rates 26% higher than counties without.2

In Missouri, local election authorities are tasked with designing and executing signature verification protocols; no state-level standards or requirements exist. Ballot curing is not required in Missouri, but local election authorities may carry out a curing process. Additionally, voters who cast provisional ballots and contact election authorities after the election must be notified whether their ballot was accepted or rejected. There is no requirement that the reason for rejection be included in that notification. (15 CSR 30-5.020, 15 CSR 30-8.020)


  1. National Conference of State Legislatures (2020) Voting Outside the Polling Place: Absentee, All-Mail and other Voting at Home Options.https://www.ncsl.org/research/elections-and-campaigns/absentee-and-early-voting.aspx
  2. Arjon, R. et al. (2020) Signature Verification and Mail Ballots: Guaranteeing Access While Preserving Integrity. Stanford Law School: Law and Policy Lab. https://www-cdn.law.stanford.edu/wp-content/uploads/2020/04/SLS_Signature_Verification_ Report-5-15-20-FINAL.pdf
  3. U.S. Election Assistance Commission (2020) Signature Verification and Cure Process.


  4. Colorado Secretary of State (2018) Signature Verification Guide.


  5. Arizona Secretary of State (2020) Signature Verification Guide.


  6. U.S. Election Assistance Commission (2016) The Election Administration and Voting Survey: 2016 Comprehensive Report.https://www.eac.gov/sites/default/files/eac_assets/1/6/2016_EAVS_Comprehensive_Report. pdf
  7. Cottrell, D., Herron, M.C., Smith, D.A. (2021) Vote-by-mail Ballot Rejection and Experience with Mail-in Voting. American Politics Research, 49(6): 577-590.
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