More than 1.8 million dead Americans remain listed as active voters, according to a study that describes the US voter registration system as "plagued with errors and inefficiencies."

The research conducted by the non-partisan Pew Center on the States also revealed that one in every eight voter records contains inaccuracies, and at least 51 million eligible voters are not registered to take part in elections.

The study released on Tuesday comes as the United States prepares for presidential and congressional elections in November.

"Voter registration is the gateway to participating in our democracy, but these antiquated, paper-based systems are plagued with errors and inefficiencies," David Becker, director of Election Initiatives at Pew, said.

"These problems waste taxpayer dollars, undermine voter confidence and fuel partisan disputes over the integrity of our elections." 

Of the approximately 24 million incorrect voter registrations across the country, or 13 per cent of the national total, more than 1.8 million of those are for people who are deceased, the centre found.

Another 2.75 million people are registered in more than one state. About 12 million records contain incorrect addresses, meaning either the voters have moved or the Postal Service would have trouble finding them, it said.

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Some of the errors can be explained by the fact that one in eight Americans moved during the 2008 and 2010 election years, mainly young people and members of the US military.

A case study carried out in the northwestern US state of Oregon showed that every new voter registration cost $7.67, as compared with just 35 cents per voter spent in Canada, which uses better technology to maintain voter lists.

The 51 million eligible voters who are not registered represents nearly a quarter of all eligible citizens. In Canada, 93 per cent of the eligible population is registered, according to Pew.

The centre said it was working with state election officials on ways to ensure greater accuracy including the cross-checking of voter lists with other data sources such as motor vehicle records and allowing voters to register online to minimise human error.