More than 300,000 names have been removed from Ireland's electoral register over the past two years, in a major push to remove duplicate names as well as those who have either emigrated or died.
The work is being undertaken by local authorities, overseen by An Coimisiún Toghcháin - the independent electoral commission - and funded by the Department of Housing and Local Government.
Speaking on RTÉ's This Week, commission chairperson Art O'Leary said: "We don't exactly know how many people are on the register that shouldn't be.
"The academic estimates vary from 200,000 to 500,000, but ... 300,000 entries on the register have been deleted in the last two years."
Watch: An Coimisiún Toghcháin's chief says 300,000 names removed from electoral register
At the same time, the number of new entries on the electoral registers has risen dramatically, in part due to the recent European, local, general and presidential elections.
Mr O'Leary said: "We also added 700,000 new voters to the register and over 600,000 people have updated their details, such as changed their addresses."
He added: "Right now, we have 31 separate registers, and they don't talk to each other and this is the essence of the problem.
"By the end of this year, we're hoping to have all of those 31 registers migrated to a single database where it will be much easier to pick up duplicates because now we have [voter] PPS numbers."
The target date for the completion of the single register had been autumn of this year, but Mr O'Leary said there had been "some slippage" in that date due to the bye-elections: "We don't like to mess with the register during an electoral process."
He said that "we should be in a much better place" by the time of the next scheduled general election in 2029.
The project has been funded by a €3 million contribution by Minister for Housing and Local Government James Browne last year.
Mr O'Leary said there would be a need for "continuing resourcing" after the establishment of a single electoral register as "the work won't end when everyone migrates".
For example, he said, his commission wants local authorities to conduct a separate audit of their register within their area as they would continue to have responsibility "for their own patch".
Last May, An Coimisiún Toghcháin published a report entitled Oversight Report on the Electoral Registers which established that 11 local authorities had more people on their electoral registers than the total number of their eligible voters.
