WASHINGTON - Curtis Napier, a 52-year-old father of two in Lima, Ohio, belongs to a much-discussed group of Americans that is far smaller than is often realized: He is a true swing voter.
He voted for George W. Bush in 2004 and for Barack Obama in 2008. With three months remaining in the campaign between Obama and Mitt Romney, Napier said, "I may not just vote for either one of them."
About one-third of Americans describe themselves as independent voters, creating a widespread impression that a large group of Americans will provide the decisive swing votes in this year's presidential election. But that impression is misleading, polling experts and political scientists say.
Many self-described independents -- close to half, according to surveys -- reliably vote for one party or the other. And many true swing voters live in states, like California or Texas, where no analyst doubts the outcome in November.
'Very small slice of people'
The actual share of voters nationally who are up for grabs is probably just 3 to 5 percent in this election, experts say. The Obama and Romney campaigns are expected to spend on the order of $2 billion, in part to try to sway this tiny share of the electorate.
"There's a very small slice of people who are genuinely undecided, but it's enough to win the presidency," said Rich Beeson, the political director for Romney's campaign.
The share of swing voters might even have declined in recent years, as many voters have become more reliably partisan. A recent report by the Pew Research Center found that self-identified Democrats are more liberal than in the past and self-identified Republicans are more conservative.
A decline in swing voters would help explain why Obama and Romney have remained within just a few points of each other, across many polls, despite a gyrating economy and attacks on both candidates.
It is still unknown whether the selection of Rep. Paul Ryan as Romney's running mate will provide him with a bump in the polls.
But so far, the Gallup tracking poll has not indicated any immediate bump, even though vice presidential choices have historically provided such a bounce.
In close races in particular, cable news pundits and enthusiastic political observers revel in swing-voter guesswork, but the ensuing portrait is often more composite sketch than photograph.
"There is so much pop psychology surrounding swing voters, but there is very little evidence that there are key demographics in the population that are inherently swing voters," said John Sides, an associate professor of political science at George Washington University.
Part of the difficulty in identifying swing voters derives from confusion about the term "swing voter" itself. These voters might describe themselves as "undecided," or as "persuadable." Often, they call themselves "independents," although many who identify that way are not.
Who are true swing voters?
Among those whose past behavior suggests they are actually up for grabs, a few demographics are especially well represented. Many will be younger, or will not have graduated from college. More will be women than men.
In three tossup states -- Colorado, Florida and Nevada -- Hispanics could make up as much as one-fifth of the swing vote. And non-college graduates will make up a particularly hefty group, about 57 percent of swing voters in battleground states this year, said one Democratic pollster, whose estimates were confirmed within a few points by a Republican.
Of likely swing voters, white non-college voters are "particularly low-information voters who don't pay attention to the daily political back-and-forth, so their opinions are driven by their economic situation," said Jefrey Pollock, the president of Global Strategy Group, one of the polling firms for Priorities USA Action, a pro-Obama super PAC. Many, he said, are "fond of the president personally, but skeptical about their economic prospects."