Washington, DC (LifeNews.com) -- A new Gallup poll shows abortion hasn't been a huge factor yet in the presidential race, but 62 percent of Americans will use abortion as a factor when they consider which presidential candidate to support. Abortion is one issue on which John McCain and Barack Obama or Hillary Clinton have big differences.

The Gallup survey, conducted May 8-11, found 13 percent of voters say a presidential candidate must share their views on abortion to get their vote.

Another 49 percent say abortion is one of many factors they will use to determine which candidate to support.

Only 37 percent say abortion is not a major issue and two percent said they have no opinion.

As has normally been the case, the abortion issue favors pro-life candidates as pro-life advocates are more likely to say they will vote for a candidate based on their abortion position.

While just 11 percent of pro-abortion voters say a candidate must share their views, 15 percent of pro-life voters say the same thing, giving pro-life candidates a four percent advantage.

On the other hand, while 39 percent of pro-abortion voters say abortion is not a major issue in the election in determining their vote, just 31 percent of pro-life voters say the same thing.

"For all five presidential elections in this period, the majority of voters citing abortion said they were supporting the Republican candidate for president. Thus, while the overall percentage of voters mentioning abortion in each case was small, the issue netted the Republican Party's candidate two to three points in the election," Gallup explained.

The number of single issue abortion voters has declined since peaking at 20 percent in 2001 while the number of voters saying abortion is not a major issue has risen to its second highest level in 11 years.

The poll found 50 percent of voters call themselves "pro-choice" on abortion while 44 percent say they are pro-life.

However, those labels don't always convey the correct position and polls that actually break down a voter's position on abortion show about 55 percent take a pro-life position opposing all or most abortions and 45 percent support all or more abortions.

The Gallup survey found older Americans over the age of 55 are most likely to call themselves pro-life.

Republicans are more pro-life than Democrats, with 66 percent of GOP voters self-identifying as pro-life. Voters in the south and Midwest are mostly likely to say they are pro-life while those in the east and west are more likely to back abortion.