SAN FRANCISCO (Reuters) - Sloppy signatures on mail-in ballots might prove to be the hanging chads of the 2012 election.
As Republicans and Democrats raise alarms about potential voter fraud and voter suppression, mail-in ballots have boomed as an uncontroversial form of convenient, inexpensive voting.
In the critical swing states of Ohio and Florida, more than a fifth of voters chose the mail-in option 2010. In Colorado, another battleground, the number was nearly two-thirds.
But there may be controversy to come. For a variety of reasons, mail-in ballots are much more likely to be rejected than conventional, in-person votes.
With the razor-close presidential election Tuesday between President Barack Obama and Republican challenger Mitt Romney potentially riding on a few tens of thousands of votes in a handful of states, the election could be decided by election officials' judgments about mail-in ballot signatures.
"You would worry that in Florida, in particular, the new hanging chad becomes whether you count this absentee ballot or not based on whether the signature is right," said Charles Stewart III, co-director of the Voting Technology Project and a Massachusetts Institute of Technology professor.
The "hanging chad" made election history in 2000 when President George W. Bush won Florida, and in turn the presidency, by 537 votes after election officials debated which absentee ballots and punch ballots with hanging flaps to count.
"In the case of Florida, a lot of absentee ballots get rejected because of signature problems. That's open for mischief," said Stewart, noting that poll workers could favor one side or the other.
Mail-in voters typically have to request a ballot, fill it out when it arrives, put it in an envelope, seal it, sign it, put it in a second envelope and drop it in the mail.
At the elections office, the outer envelope is opened and the signature verified, and if it's judged to be valid the ballot goes into safe-keeping for counting.
Many states attempt to contact the voter if there is any issue with the ballot. Election officials in states with deep experience in mail-in voting - especially Oregon and Washington state, which rely on it entirely - say they have honed the process to reduce invalid ballots to a minimum.
But in many other states the process is not as fast or simple as talking to someone at a polling station. National law requires equipment at voting stations that informs voters of ballot issues and lets them fix them; fix-it opportunities are not mandated for mail-in ballots.
As a result, mail-in ballot voters who manage to get a ballot to election officials are about four times more likely to see their vote go uncounted as those who vote in person, Stewart calculates.
Add in the number of ballots never sent to voters who request them and ballots that don't make it to the polling station, and approximately one in five mail-in votes may be lost, Stewart says.
How absentee ballots are counted can affect outcomes in the most important of races. Minnesota Senator Al Franken won his seat in 2008 by 312 votes after a fight over absentee ballots.
Jeff Clemens, a Democrat recently declared winner of a Palm Beach County Senate primary that had been the subject of several recounts and a court case due to alleged absentee ballot fraud, said Florida needs to reevaluate how it handles mail-in ballots.
"There's no question that the absentee ballot process as it stands is a potential disaster," he added.
Voters like the convenience of making decisions at their own pace, in their homes, and election officials say it costs less to operate a mail-in system. Officials say it also boosts turnout, especially in lower profile elections, when the fate of a school board official might justify a few minutes with the mail, but not an hour's trip down to a polling station.
But Ohio rejected more than 14,000 mail-in ballots in 2010, or 1.7 percent of those sent in domestically, and Florida rejected close to 18,000, or 1.4 percent, according to the federal Electoral Assistance Commission survey. Both topped the national average of 1.3 percent. In Colorado, rejected absentee ballots made up 0.43 percent of the total cast in the election.
In Colorado, where polls show a dead heat in the presidential election, officials' decisions about which ballots to reject could easily determine which way the state goes.
Some election researchers say vote-by-mail is inherently problematic, because it does away with the iron-clad guarantee of a secret ballot. That's a problem for an individual who wants privacy but can't get it, such as a partner in an abusive relationship. It also makes vote-buying much easier, since purchases can make sure they get what they buy.
That has not been much of a problem so far, but it has happened. In Miami, a mayor's race in 1997 was overturned by a court, which threw out 5,000 absentee ballots in the face of evidence of illegal activity including forgery and coercion.
"I think it is somewhat serious in actuality, and it's quite serious in potential," said Daniel Lowenstein, an election law specialist and emeritus professor of law at UCLA.
So can vote-by-mail be done right? Election officials in Washington state and Oregon say the keys are to use statewide databases when registering voters, to train workers in forensics and manually check every signature and to contact voters whose ballots don't pass, giving them enough time to correct problems.
Oregon even sends pairs of voting assistance workers, from opposing parties, to nursing homes as a way to avoid such pressure. Oregon throws out half as many mail-in ballots as the states likely to determine the president this year.
Oregon Secretary of State Kate Brown, who won her first state primary election by seven votes, argues that her system is better than a hybrid offering voters polling stations as well as mail-in ballots.
"One of the challenges for states that have both absentee and polling place elections is that there is a lack of consistency in the process," she said.
Oregon approved going to exclusively mail-in-ballots in 1998, and it has cut rejections to an average of 0.64 percent of ballots in the last five elections, Brown says.
Oregon turnout of registered voters in the 2008 presidential race was third in the nation at 85.7 percent, which the state says is the best measure of vote-by-mail's success.
Washington state came more recently to vote-by-mail. It rejected more than 2 of every 100 ballots in 2008. But the state cut that rate by a third in 2010, which State Elections Co-Director Shane Hamlin credited to massive voter education.
Signature issues and late ballots are the two main issues in Washington, like most states. "They are both totally fixable through education," he said.
In Ohio, more than a million absentee ballots have arrived at elections offices so far. Secretary of State spokesman Matt McClellan describes a long series of actions taken to ensure mail-in ballots are counted, including contacting voters whose ballots are problematic.
An Obama campaign spokesman acknowledged the importance of making sure mail-in ballots are handled properly and said the campaign would have observers in key areas. The Romney campaign did not respond to a request for comment.
McClellan said the state was trying to balance accuracy and access, a theme echoed in states across the country eager to raise participation rates and see mail-in as one way to do so.
"It fits the 21st century lifestyle," said Washington state Secretary of State Sam Reed.
Additional reporting by Tom Brown in Miami; Editing by Jonathan Weber, Mary Milliken and Todd Eastham