Joshua Lott / Reuters A member of the United States National Guard patrols along the U.S. and Mexico border in Nogales

From Arizona to Amsterdam, immigration remains one of the most contentious and divisive debates for Americans and Europeans alike. It is also, it seems, a debate fueled by large-scale misconceptions on both sides of the Atlantic. A new survey released Thursday has found that Americans and Europeans both tend to greatly overestimate the immigrant population in their home countries  but, when armed with accurate population figures, they hold significantly more lenient views towards migrants.

In the U.S., for instance, the average resident believes that 39% of the U.S. population was born abroad; the real figure is less than 14%. When told the correct figure before they answered a question about acceptable immigration levels, however, respondents were 20% less likely to say that there are "too many" immigrants in their country than residents who weren't primed with the accurate stat. Similar discrepancies exist in the U.K., France, Germany, Italy, the Netherlands and Spain, according to a survey of 6,000 people in the U.S., Canada and six European countries carried out by the U.S.-headquartered transatlantic think-tank The German Marshall Fund (GMF). (See pictures of immigration in Europe.)

Americans are also ill-informed about illegal immigration; 58% of those polled said that most immigrants did not have legal residency. In fact, illegal immigrants comprise less than one-third of the migrant population in the U.S.

These results, experts say, show what a vexing issue immigration can be for policy makers both in Europe and the U.S, where concerns over labor-market competition, assimilation and crime have led many citizens to demand tougher immigration laws and enforcement. In the GMF survey, majorities in the U.S. (73%), the U.K. (70%), Spain (61%), France (58%) and the Netherlands (54%) felt their government was doing a poor job managing immigration. (See pictures of immigrants detained in Arizona.)

"This discrepancy is clearly a problem," says Susan Martin, the director of the Institute for the Study of International Migration at Georgetown University who reviewed the survey results before publication. "It's hard to measure the appropriate response to calls among your constituents to drop the admission numbers for immigrants if people would be happy if they knew how many people were actually coming in. So the lesson here should be that there is so much more we can do to inform the public about immigration trends."

The survey also reveals how Europeans and Americans hold different anxieties surrounding immigration. Americans tend to worry about the economic effects, while European concern centers around the integration of immigrants into their host nation's culture. Around two-thirds of U.S. respondents felt that immigrants benefit more from social-security measures than they contribute in taxes, for instance, which was significantly higher than most European countries included in the poll. Europeans, on the other hand, are concerned that immigrants  particularly Muslims  are not integrating well. Only 41% of Germans felt that immigrants were well-assimilated into German society, and that figure dropped to 25% when participants were asked specifically about Muslim immigrants. Almost 60% of Americans, on the other hand, felt that immigrants have integrated well into U.S. culture. (See pictures: "A Murder by the Border.")

Claudia Diehl, a professor of immigration at the University of Goettingen in Germany, says that the survey results show that the U.S.'s experience with immigrants should help ease European concerns about Muslim integration  in time. "Americans are much more optimistic about immigrant integration, especially of second-generation migrants, including Hispanics," she says. "This confidence reflects a historic experience with many generations of immigrants that many Europeans are missing."

The survey also found that the personal experience of economic hardship correlates with concerns over immigration. Those whose household economic situation got worse in 2010 were more likely to say that immigrants take jobs away from native-born workers. In the U.S., for instance, 63% of those who faced a pay cut or job loss in 2010 felt immigrants threatened job availability, compared to 49% of respondents whose economic situation either improved or stayed the same. Unemployed Europeans were also more likely to say that immigrants take their jobs (43% compared to the total European average of 35%). (See pictures of immigration in Greece.)

But at the same time, the economic gloom of 2010 did not seem to shift overall perception of immigration in any country  in fact, it improved the way Americans and Europeans see immigrants, albeit marginally, as measured by the broad-brush question: "Are immigrants more of a problem than an opportunity?" Many commentators have claimed that the global financial crisis resulted in the rise of far-right, xenophobic parties in Europe in 2010. But, says Diehl, "this survey shows that the simple calculation that anti-immigrant sentiment is primarily driven by economic competition is not working very well."

Following the debate in the U.S. on the controversial SB1070 Law in Arizona, which made illegal immigration a state as well as federal crime, Americans questioned in the survey were split on whether responsibility for enforcing immigration law should rest with local or federal authorities: 44% favored state police, while 50% favored federal cops. Enforcement, of course, is only one element of immigration policy, even though it dominates the debate more so than questions over how to attract talented and industrious immigrants into the economy. That might change, according to Martin of Georgetown University, if people could be given a realistic sense of the scale of immigration in their country. "When they do have real knowledge  when they have the stats in front of them  this survey and others show that Americans and Europeans actually tend to have a nuanced view toward immigration."

See a video of illegal immigration by sea.