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How do we know how many people cross the border illegally?

On this week's episode of the "Where Did You Get This Number?" podcast, host Anthony Salvanto explores U.S. immigration statistics, how they're derived, and what they mean for the country. 

Listen to this episode on Stitcher

Public opinion on whether immigrants are a burden or strength to the country have changed significantly during the past 20 years, according to Mark Hugo Lopez, director of global migration and demography research at the Pew Research Center. 

"So for example, back in the '90s, two-thirds of Americans would have seen immigrants, or said immigrants were a burden to the country because they take jobs, health care, etc." said Lopez. "Today on the other hand though, about two-thirds of Americans will say, or more than half I should say, that immigrants are actually a strength for the United States because of the talents that they bring."

Pew surveys have also found that there seems to be some sort of connection between knowing or living close to immigrants and having a more positive view of immigrants.

"So these results that we found about Republicans living near the border having a somewhat different point of view does reflect as a general finding that the closer you are to immigrants or immigrant communities, the more likely you are to have a different view of immigrants than somebody who lives farther away," Lopez said.

About one-quarter of the over 40 million immigrants in the United States are unauthorized, and one of the main ways that figure has been calculated is with birth and census records from other countries, according to Randy Capps, director of research at the Migration Policy Institute. Capps referred to the years when most of the unauthorized immigrants coming into the country were from Mexico.

"We have good birth records [from Mexico] and we can add up that and compare it to the Mexican census, and that could tell us how many Mexicans could potentially have left the country and come to the U.S.," Capps said. "And the other benchmark is how many people might have entered the country illegally across the border with Mexico or might have come in legally, but then decided to overstay their visa." 

Capps also said that there is a misconception that Mexico is sending the most unauthorized immigrants now.

"The big Asian countries of China and India are sending more people to the U.S. each year now than Mexico," Capps said. "Also, it's not just a matter of the border. Probably 60, 70 percent now of the unauthorized immigrants in the country are coming in by overstaying their visa, not by crossing the border." 

To hear more of our discussions on immigration in the United States, download the "Where Did You Get This Number?" podcast on Apple PodcastsGoogle PlayStitcher, or Spotify. New episodes are available every other Monday.

Producers: Ian Flickinger, Allen Peng

Host: Anthony Salvanto