Both sides in the rancorous debate over changing Ohio’s election law lack facts to back up their passion. In that case, election law experts say, it’s up to those who want to make it harder to vote to come up with the proof.

The Senate is set to vote next week on a 400-plus page bill changing everything about elections from registration to recounts. A change added last week requires Ohioans to show identification when they register to vote and again at the polls.

Republicans who control the Legislature say the change is needed to prevent voter fraud. Democrats, who walked out of the committee recommending the bill rather than vote on a measure they find odious, say the requirement will scare away minority, poor and older voters.

There are no studies showing either rampant voter fraud or rampant voter suppression in states with ID requirements, according to Electionline.org, a nonpartisan Washington-based group that studies election law.

‘‘There’s this myth of voter fraud out there that has yet to be substantiated by any kind of data,’’ said David Becker, a Washington-area attorney who until early this year worked in the civil rights division of the U.S. Department of Justice.

Documented fraud cases almost always involve mail-in voting, said Daniel Tokaji, a law professor at Ohio State University.

‘‘You don’t fix what’s not broken,’’ he said. ‘‘It’s not necessarily a bad idea to make it a little more difficult to register, if the trade-off for that is to actually make it easier to show up at the polling place.’’

Instead, the Ohio proposal will lead to more provisional ballots, which mean long lines and confusion at the polls, Tokaji and others said. County election officials warned lawmakers that more provisional ballots, which aren’t counted until after Election Day, could delay results in close races.

‘‘Voters have concerns about the ways provisional ballots are counted in general, and in Ohio in particular,’’ Becker said.

Lawmakers voted this fall to allow any Ohio voter to get an absentee ballot without having to provide a reason — and imposed ID requirements. Tokaji opposed the measure as opening up opportunities for fraud, because there’s still no guarantee someone else doesn’t observe or influence how the voter fills out the ballot.

The federal Help America Vote Act already requires identification for first-time voters who registered by mail and didn’t verify their ID in that process. Also, 21 states require some form of identification to vote. Of those, six specifically ask for photo ID, including Indiana, where the law takes effect in January. A federal court barred enforcement of Georgia’s photo ID law.

Most of the requirements have come about since the 2000 election, said Nathaniel Persily, a University of Pennsylvania law professor. Becker noted that nearly all have been in states with GOP-dominated legislatures.

‘‘I am troubled by any law that deals with voting access or fraud that is favored by one party and disfavored by the other,’’ Persily said.

Democrats also have little data to back up their arguments. Experts say it’s true that blacks and the poor are least likely to have photo identification, but no one has studied how voting patterns change in the states that also allow other forms of ID such as bank statements or Medicaid cards.

‘‘To give Ohio credit, they’ve tried much harder to alleviate those concerns than a lot of states,’’ Becker said.

Putting all those arguments aside, Persily said, Ohio should look at the real problems of the 2004 election: long lines, confused voters and vastly varying patterns of how provisional ballots were cast and counted from county to county.

‘‘The point is, the more technical the legal infrastructure, the more sophisticated the poll workers have to be,’’ he said. ‘‘Now you have a 400-page election law. You will have poll workers who, when confronted with a legal form of ID, will say, ’No, you get a provisional ballot.’’’

Carrie Spencer Ghose is a correspondent for the Ohio Associated Press’ Columbus bureau.