Candidate qualities: Three in 10 who participated in the caucus said it was most important to choose a candidate who could defeat President Barack Obama in November, but 25 percent thought it more important for the candidate to be a true conservative and 24 percent said the candidate must have strong moral character. Experience — an attribute that figured prominently in sparring between Mitt Romney, Newt Gingrich and Herman Cain before surges lifted Rick Santorum and Ron Paul — was cited by 16 percent.

Speaking of surges: About half of Iowa caucus-goers said they made up their minds in the last few days, and 34 percent of them backed Santorum. Romney was second among this group with 23 percent.

Young voters and new participants: The youngest voters backed the oldest candidate. Those under 30 broke heavily for Paul, with the 76-year-old Texas congressman also holding a 10-point advantage among those attending their first caucus.

Tea party: Tea party backers made up about two-thirds of Iowa caucus-goers, and they broke 29 percent for Santorum to 19 percent each for Romney and Paul. Among the 1 in 10 voters who opposed the tea party, Romney led with 43 percent of the vote.

Minding the money: Voters who called the economy the top issue backed Romney over his top competitors, while those most deeply concerned about the federal budget deficit gave Paul a 7-point edge.

Evangelicals and conservatives: Two groups frequently cited as key to victory in Iowa were assets to Santorum’s late surge. He was the only candidate to top 30 points among evangelicals or those who consider themselves “very conservative.” As in 2008, evangelicals made up about 6 in 10 caucus-goers and about half described themselves as “very conservative.”

Independents: They have grown as a share of the electorate from 2008 and now make up about a quarter of voters. Forty-three percent preferred Paul, compared with 19 percent for Romney and 13 percent for Santorum. Among those who consider themselves Republicans, Romney and Santorum ran about evenly.

The survey was conducted for The Associated Press and the television networks by Edison Research as voters arrived at 40 randomly selected caucus sites in Iowa. It involved interviews with 1,787 caucus-goers and had a margin of sampling error of plus or minus 4 percentage points.