Here's one more way swing states stand out: Their citizens are more likely to vote.

Thatmay not be surprising given, in this year's presidential campaign, thebattleground states were deluged by TV ads and targeted forsophisticated get-out-the-vote operations. After all that, 10 key swingstates had significantly higher turnout than the rest of the USA, ananalysis of data by the non-partisan Center for the Study of theAmerican Electorate shows.

That turnout gap is growing, withpotential repercussions for candidates down the ballot and the sense ofconnection some Americans have with their government.

"Increasingly,people in non-swing states don't think their vote makes anydifference," says Curtis Gans, director of the center. That seems to becosting non-battleground states some of the boost in voter participationthat presidential contests traditionally bring.

It is adistinctly American phenomenon. Because of the Electoral College system,presidential candidates now essentially ignore states that are solidlyRepublican or Democratic. They focus instead on the dwindling number ofstates that might swing one way or the other.

As recently as 1996, there was essentially no difference in turnoutbetween the swing states and the other states plus the District ofColumbia: 51.5% of eligible citizens in the battlegrounds voted;elsewhere, 51.4% did. In that campaign, the presidential candidatescontested more states and their TV ads aired more broadly.

Differencesin turnout have been steadily widening since then: 1.2 percentagepoints in 2000, 4.4 points in 2004 and 5.2 points in 2008. This year,64.2% of eligible citizens went to the polls in the battlegroundscompared with 56.8% in the rest of the nation - a disparity of 7.4points.

The battlegrounds used in this analysis are Colorado,Florida, Iowa, North Carolina, New Hampshire, Nevada, Ohio,Pennsylvania, Virginia and Wisconsin. All were targeted by PresidentObama and Republican Mitt Romney in 2012, although the list of swingstates would have been somewhat different in each of the previouscampaigns. (That makes the trend line more illustrative than precise.)

The conclusion by citizens in non-battleground states that their votedoesn't really matter could "add to the sense that some voters feelleft out of politics," Democratic pollster Margie Omero says. calculatesthe turnout gap is likely to hurt Democratic candidates more thanRepublican ones because the people most easily discouraged from votinginclude such Democratic-leaning groups as racial minorities and youngpeople.

"The good news is some of the new efforts at increasingturnout seem to be working: The ads, the person-to-person contact, theearly voting," Omero says. Although residents in swing states in 2012often decried the onslaught of TV ads, most of them negative, thecommercials apparently did more to boost turnout than to turn offvoters.

Gans says the findings strengthen the case for modifyingthe nation's unique political system so candidates have a reason tocontest more states - perhaps by distributing Electoral College votesproportionately rather than winner-take-all in a state, or by allocatingthe votes by congressional district rather than statewide. Maine andNebraska already do that.

Nationwide, 58.75% of eligible citzensvoted in 2012, down from 62.29% in 2008. The turnout rate rosesignificantly in the District of Columbia, which permitted same-dayregistration. There was a rise in Massachusetts, presumably because ofits hotly contested Senate race between Republican Sen. Scott Brown andthe victorious Democratic challenger, Elizabeth Warren.

Turnoutedged up a tick in Iowa, Colorado and Louisiana and fell everywhere else- by 1.9 points in battleground states and 4.1 points innon-battleground states. It dropped 8.52 points in New York and nearly 5points in New Jersey, states that had been hit hard by Superstorm Sandytwo weeks before Election Day.