U.S. presidential candidate Donald Trump, right, and Mexican President Enrique Peña Nieto prepare to deliver a news conference in Mexico City on Aug. 31. (Yuri Cortez/AFP/Getty Images)

Americans consistently mention immigration as one of the nation’s most pressing political concerns, and it has become a signature issue in the presidential campaign. On Wednesday, Donald Trump flew to Mexico to meet with the country’s president, and capped off the day by giving a fiery speech in Phoenix on fighting illegal immigration.

But while many Americans consider immigration one of the biggest issues for the future president, surveys suggest that they also have little understanding of the scale of the problem.

In fact, it’s remarkable just how much Americans overestimate immigration in their country, as a fascinating 2015 survey by global market research company IPSOS demonstrates. On average, surveyed Americans guessed that one-third of people in their country were immigrants. The actual figure? Only 14 percent.

The United States wasn’t alone in this tendency to exaggerate. As the chart below from the data blog Metrocosm shows, Japan, Poland, South Korea, Hungary, Italy and Belgium had more outrageous guesses than the United States did about the percentage of their population made up by immigrants.

This chart from IPSOS similarly shows that this is a tendency shared around the world — roughly a dozen developed countries surveyed are all above the dashed line in the chart below, indicating that they guessed too high on the percentage of immigrants in their country. Again though, the United States is toward the top.

American estimates for the size of the Muslim population in this country, also a focus of political discussion, are even more extreme. In the IPSOS survey, people on average guessed that 15 percent of the U.S. population is Muslim, compared with an actual figure of 1 percent.

Again, the United States is hardly alone in this regard. Hungary, Poland and Japan overestimate the presence of Muslim populations in their countries by far greater amounts. But the United States ranked among the top in the developed countries surveyed.

These surveys asked about immigration in general, rather than illegal immigration. And it’s true that a lot of people are generally inaccurate on data points about their country, from the percentage of wealth owned by the wealthiest 1 percent in the United States (37 percent) to how many Americans are overweight or obese (66 percent).

But with immigration, it’s revealing that people’s mistakes tend to skew so far in one direction: Almost no developed country underestimates its level of immigration.

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