The Times said voters appear to have been purged by mistake and not because of any intentional violations by election officials or coordinated efforts by any party.

States have been trying to follow the Help America Vote Act of 2002 by removing the names of voters who should no longer be listed. But for every voter added to the rolls in the past two months in some states, election officials have removed two, a review of the records shows.

The newspaper said it identified apparent problems in Colorado, Indiana, Ohio, Michigan, Nevada and North Carolina. It says some states are improperly using Social Security data to verify new voters' registration applications, and others may have broken rules that govern removing voters from the rolls within 90 days of a federal election.