TALLAHASSEE — Nearly 5 million people in Florida who are eligible to vote aren't registered, according to a nationwide nonpartisan group that helps improve the accuracy of state voter rolls.

The Electronic Registration Information Center also estimates that there are also nearly 1 million problematic registrations in Florida. They are people who are registered in another state, two Florida counties, or who have died or changed their names.

ERIC is a 7-year-old consortium of 20 states and Washington, D.C., that fosters the sharing of registration data to track voters' movements between states, cities and counties.

The group cross-checked the driver's license database against the statewide voter roll. ERIC estimates there are 4.6 million people 18 and older who can drive but can't vote.

"That's a massive number," said John Lindback, ERIC's executive director. "It's the equivalent of a moderate-sized state."

The estimate includes two large groups that can't vote in Florida even if they wanted to: noncitizens and felons.

Although ERIC doesn't estimate the ineligible voters, other groups have.

The Brennan Center for Justice at New York University School of Law is a public policy institute that supports restoring the right to vote for felons, modernizing voter registration and eliminating strict voter ID laws. It estimates there are 1.7 million adults of voting age who are ineligible to vote because they are felons who have been removed from the rolls.

That's more than any other state and about one-fourth of the 6.1 million felons nationally who are ineligible to vote. The Brennan Center estimates that in Florida overall, those who lost their right to vote because of felony convictions make up about 10 percent of the state's voting-age population.

Florida has more than 13 million registered voters. ERIC's estimate of Florida's unregistered voters represents one-fourth of the state's adult-age population.

States who joined ERIC are required to conduct outreach programs at taxpayer expense every two years to encourage people to sign up to vote.

Florida does not send mailings to people who are not registered to vote. Those efforts are done by political parties or third-party groups, such as the League of Women Voters.

Colorado's state elections director, Judd Choate, said that ERIC mailings have boosted the state's share of eligible registered voters to 91 percent, while reducing the number of flawed registrations.

"Our voter lists are as clean as they've ever been," Choate said. "It saves us a tremendous amount of money, and it's made us better stewards of our state on behalf of the citizens."

Colorado offers same-day voter registration, which means anyone can show up and vote — even if they are not already registered. In Florida, the voter registration books are closed 29 days before an election.

Florida's 67 county election supervisors aggressively lobbied the Legislature this spring to make Florida the next ERIC state, but to no avail.

Although the bill passed the House unanimously, it died in a Senate committee in the closing days of the regular session — a decision that Chris Chambless, the supervisor in Clay County and president of a statewide supervisors group, called "a shame."

ERIC's preliminary report in Florida, done in March and presented to state elections officials, projected that 717,000 voters had double registrations because they moved within the state, while 233,000 had them because they moved from Florida to another ERIC state.

An estimated 24,000 people who had died were projected to still be registered, and 17,000 people were found to have duplicate registrations, which can be cases in which a voter's name changed due to a marriage or divorce.

Florida has nearly four times as many voters as Colorado. The two states are alike in that they both have large immigrant populations and consistently have close, competitive elections.

"We're a purple state, just like you," Choate said.

Florida Gov. Rick Scott's chief elections official, Secretary of State Ken Detzner, did not dispute ERIC's numbers.

Detzner's office said it works thoroughly to improve the accuracy of Florida's voter registration database.

"The department uses a variety of methods to ensure accurate voter registration rolls," the agency said in a statement. "For example, we compare information received from the Department of Health and the Social Security Administration master death file to identify voters who are deceased."

The agency said that everyone who registers to vote in Florida must provide a driver's license number or state ID card number or Social Security number, which are cross-checked with the state Department of Highway Safety and Motor Vehicles database or the Social Security Administration.

Detzner's office said only supervisors of election have the authority to remove an ineligible voter from the rolls.

Florida is not the only big state that has not joined ERIC. California, Texas and New York also are not members.

The price for Florida to join the consortium is $71,500 a year.

Times senior news researcher Caryn Baird contributed to this report. Contact Steve Bousquet at bousquet@tampabay.com. Follow @stevebousquet.