But databases are prone to errors such as misspellings and transposed numbers, and applicants are prone to make mistakes or write illegibly on applications. The Social Security Administration has acknowledged that matches between its database and voter-registration records have yielded a 28.5 percent error rate.
States vary in how they treat applicants whose records don't match, and experts say rules in some states could prevent thousands of eligible voters from casting ballots or having their votes counted in November. Those who don't match in Oregon, for example, can cast a ballot, but their vote for president or any other federal race on a ballot won't be counted. There are currently about 9,500 voters in Oregon who fall into this category, but a state spokesman says matching issues will be resolved with most of them before November so they can vote in federal races. Fewer than 500 voters were affected by this during the state's primary.
"One of the big problems is that states just haven't been very transparent about how they're operating their new database," says Dan Tokaji, law professor at the Ohio State University's Moritz College of Law. "So it's really hard to tell how this is going to play out. A few states have implemented overly stringent matching rules, the consequence of which could be that some citizens' votes don't get counted."
In the 2000 election, about 1.3 million registered voters said they didn't vote due to trouble with their registration, according to a U.S. Census Bureau survey, which didn't elaborate on the nature of the troubles. In an election when record numbers of new voters are expected to participate, experts say the number of voters who find they can't cast a ballot this year could be higher.
Voter registration databases are central to the democratic process in every state except North Dakota -- which doesn't require registration. Everywhere else, the registration roll is the gatekeeper determining eligibility to vote in an election. Voter lists aren't used just for elections, however. Shortly after the Sept. 11 terrorist attacks in 2001, before statewide databases were mandated, then-Attorney General John Ashcroft reportedly ordered that voter registration lists be checked for links to terrorists.
Until HAVA, each county or election district in most states maintained its own voter list, which often resulted in duplicate registrations when voters moved and re-registered -- creating opportunities for fraud. States were supposed to consolidate their lists by Jan. 1, 2004, but most got an extension to 2006. Creating a statewide system that interfaces with multiple county registration databases built by different companies proved to be difficult. About a dozen states missed the 2006 deadline, and four were sued by the Justice Department.
There have also been a number of issues involving companies that make the systems. Some states built databases in-house; others outsourced to companies like Election Systems & Software (which also makes voting machines), and the Bermuda-based Accenture. Accenture was hired by several states, but lost contracts in all but one for missed deadlines and other issues.