Immigration reform has become a contentious issue in the U.S. this year, and a new poll revealed Americans hold varying positions on immigration. Pictured: Donatila Diego, (left) and Juana de Leon, both originally from Guatemala, showed their support for the Obama administration's immigration reform plan, on July 9, 2015, in Homestead, Florida. GETTY IMAGES

Immigration reform has emerged as a central issue in the 2016 presidential election as more and more candidates include their stance on the issue as part of their political platform. So what do Americans as a whole think of immigration?

Here's what Gallup has discovered. Only 25 percent of the country prefers an increase in immigration, more than double the 12 percent in a similar June 2002 study, a new Gallup study published Monday revealed. Some 34 percent feel that fewer immigrants should be granted entrance to the country, according to about 40 percent of respondents to this year's survey.

The results were part of Gallup's Minority Rights and Relations survey conducted from June 15 to July 10, which included greater representation of black and Hispanic citizens in the sample than in past years. Known as "over-sampling," the practice involves taking a "closer look at attitudes and opinions of minority groups whose representation in the sample of a standard poll might otherwise be too small for statistical analysis," according to the study. All 2,296 respondents were older than 18; all were interviewed by phone.

Through the lens of race, respondents' positions on immigration varied greatly. Hispanic respondents, half of whom reported being immigrants themselves, were most likely to prefer increased immigration at 36 percent. At the other end of the scale, non-Hispanic white citizens displayed the lowest support for more immigration, with only 21 percent. African-American voters fell between the two with 30 percent in favor of higher immigration rates.

However, all three groups reported their highest support for increased immigration rates since the 9/11 terrorist attacks in 2001, the study found.

U.S. Immigration Summary | InsideGov

The presidential candidates' stances on immigration reform this election season reflect the study's diversity in opinion. Immigration issues dominated the GOP debate Thursday, and the candidates gave varying responses to how they plan to address undocumented immigrants.

“There should be a path for earned legal status for those who are here,” former Florida Gov. Jeb Bush said. “Not amnesty -- earned legal status.”

Real estate mogul Donald Trump, who credits himself with starting the presidential candidates' campaign trail conversation about immigration reform, reiterated remarks he has made before about wanting to build a border between the country and Mexico.

“We need to build a wall, and it has to be built quickly,” Trump said. “And I don’t mind having a big beautiful door in that wall so that people can come into this country legally.”