COLUMBUS, Ohio — The clock was ticking for Jen Miller.
The state of Ohio had released names of 235,000 voters it planned to purge from voter rolls in September.
Ms. Miller, director of the League of Women Voters of Ohio, believed thousands of voters were about to be wrongly removed.
Over the summer, the Ohio secretary of state had sent her organization and others like it a massive spreadsheet with the 235,000 names and addresses that would be purged from the state’s voter rolls in just a month — a list of people that, state officials said, some part of the bureaucracy flagged as deceased, living somewhere else or as a duplicate. The League of Women Voters had been asked to see if any of those purged qualified to register again.
Ms. Miller, who spends her work day helping register people to vote, scrolled through the names and then asked herself a question: What was her own voter status in the state?
She went online and discovered that her name had also been flagged as an inactive voter. The state was in the process of removing her from its voter rolls.
“I voted three times last year,” said Ms. Miller. “I don’t think we have any idea how many other individuals this has happened to.”
Ohio, where the Democratic presidential candidates are set to debate Tuesday, is both a battleground state and the site of some of the country’s strictest voting laws, from voter ID requirements to a “use-it-or-lose-it” provision that lets officials drop voters seen as inactive.
The combination has led voting rights advocates to contend that parts of the state are regularly disenfranchised, largely in purges aimed at those who have died or moved away, but which also hit real voters who don’t learn they can’t vote until Election Day. Election officials in other battlegrounds such as Florida, North Carolina, Georgia and Texas regularly purge their voter lists as well.
This year, a group of elected officials in the state, mostly all moderate Republicans, tried to answer the concerns with an experiment of their own: Rather than purge the voter rolls behind closed doors as had been done in the past, the government released the full list of those to be removed this summer, and gave the list to advocacy groups. The groups said they found the list was riddled with errors.
The result: Around 40,000 people, nearly one in five names on the list, shouldn’t have been on it, the state determined. And it only found out before anyone was actually turned away at a polling place largely because of volunteer sleuthing.
Few people had expected a problem at that scale.
But the process gave hope to people working on voting rights, who for years had pushed the state to be more transparent in how it was maintaining its voter rolls. Moderate Republicans, caught between advocacy groups pushing for fewer purges and more conservative leaders in other states urging for more, think they may have found a way to thread the needle.
“We’re talking about crowdsourcing, in simply putting the list out there,” said Frank LaRose, Ohio’s secretary of state, whose office oversaw the purge and who manages the election here.
Ohio’s needle-threading experiment this year — the only time advocates say a state government has released a list ahead of time — also offers one of the first looks at how so many names could be incorrectly removed from the rolls.
In one case, a data mistake from an outside firm meant a large number of people’s names were set to be knocked off. Ohio’s 88 counties each used a different process of removing people from the rolls, an immediate source of headaches for officials trying to compile a statewide list.
And voting rights groups found an unexplained tranche — around 20,000 people — who had been marked to be purged because of inactivity in future election cycles, but were actually active voters in previous Ohio elections. These voters were in Franklin County, a Democratic stronghold in the state.
Under Ohio law, the state is allowed to cull voters’ names from the rolls if they haven’t voted in six years and don’t respond to a postcard from the state informing them that they are about to be purged and need to take action. Voting groups challenged the law in court saying such rules suppress the vote, but the Supreme Court, in a 5-4 decision last year, disagreed and found finding so-called use-it-or-use-it laws constitutional.
“If you look at the numbers, it’s hard not to be jaded by this,” said Steve Tingley-Hock, who runs a watchdog group called the Ohio Voter Project and initially discovered the error.
How Mr. Tingley-Hock, a volunteer who doesn’t work for the government, chanced upon such a big mistake shows the kind of unusual backstop the state now depends on to carry out its work correctly.
A database consultant by trade, Mr. Tingley-Hock in recent years developed a hobby of spending his weekends downloading the state’s voter data onto his own laptop where he manages a database that keeps track of every voter in Ohio.
“Someone needed to keep a record of what’s happening in the voter population,” said Mr. Tingley-Hock, who thinks the purges are targeting certain demographic groups, especially young voters. “If you want to know what I’m doing on a Saturday morning, it’s downloading these files from the state.”
Working on a shoestring budget and donations from relatives, he keeps track of similar data from six other states, including North Carolina and Florida, which have both been criticized for voter restrictions.
When Mr. LaRose’s office released the spreadsheet with the list about of 235,000 names to be purged, Mr. Tingley-Hock ran them through his own database and found thousands of names matching active voters.
“It’s a simple query if you have a database management system,” he said. “A guy at his dining room table can figure this stuff out. It’s not rocket science.”
Many conservatives in the state argue that the purges and voting restrictions are necessary to prevent people from casting ballots illegally.
“There can be ballots not cast in a legitimate manner by legitimate people,” said Senator William P. Coley II, a Republican who has pushed for tightening the voting laws. “The number of elections that are decided by one vote or a few votes — it doesn’t take much to throw an election.”
That view could create difficulty for moderates like Mr. LaRose. As the state’s top election official, he has found himself at odds with Republican colleagues in acknowledging there is no evidence that voter fraud has ever been widespread.
Asked if officials outside of Ohio would follow his lead in releasing lists ahead of time, he said he didn’t want them to “take the wrong lesson” from fixing problems in a voter purge.
“I hope that other states don’t look at what we’ve done and say, ‘We’re not doing it,’” he said.
For the time being, the government’s efforts at transparency have garnered the praise of some of its frequent critics.
André Washington of the A. Philip Randolph Institute, an African American unionist organization that sued the state in the case the Supreme Court ruled on last year, said this was the first time the government was “willing to work with organizations like mine” and said he hoped other states would follow Ohio’s path.
But he wasn’t convinced advocacy organizations on their own were enough of a watchdog to ensure that the voter lists were accurate.
“If we glanced at it and found mistakes ourselves, there could be thousands more,” he said.
The experience has left some voters like Jennifer Kulina-Lanese, a former veterinary professional, shaken. She got a call from the League of Women Voters shortly after it received the list, informing her that the county where she had voted just last year had started the process for her to be purged.
“I still don’t know why, and that’s what’s scary,” said Ms. Kulina-Lanese, who is 45. “The idea that Franklin County was starting a process to remove me was terrifying.”
She added: “I would have shown up to vote, and I don’t know if I would have been denied.”