Who Are the 11 Million Undocumented Immigrants?

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They've come here to settle down.

"The unauthorized immigrant population is, to a degree that I think that is largely unappreciated, a group of families with children," Passel says. Twenty-one percent of nonimmigrant households are couples with children. In other words, nuclear families. In households of illegal immigrants, that number jumps to 47 percent, according to 2008 data.

"More than half of the adult men are in families, are married, or have a partner," he says. "And most of them, 80 percent of that half, have children here. The women represent about 40 percent of the adults, and almost all of them are not here by themselves." Part of this is due to difference of ages in the sample. The undocumented families are younger, and therefore more likely to have children. Nonetheless, the data is indicative of people who have come here to raise a family.

With the announcement of bipartisan legislation that would allow a pathway to citizenship for undocumented residents, the number 11 million becomes important. That's the most commonly cited estimate of the number of illegal residents in the country. But where does this number come from?

The number can be traced to the work of Jeffery Passel, a senior demographer at the Pew Hispanic Center. But more than the size of the illegal populations, Passel has found ways to document details of how the group lives and works, even though no direct survey of illegal immigrants exists.

To find these undocumented people, Passel has to do some detective work. Here's the basic process: For one, we know the number of immigrants the country allows in through the legal process. Also, we know, from the U.S. Bureau of Labor Statistics, how many people in the United States were born in another country. So the formula for finding the number of illegal immigrants in the country becomes, essentially, simple arithmetic.

"It's immigrants in the survey, minus legal immigrants, equals unauthorized immigrants in the survey," Passel says. It's actually a bit more complicated than that, involving a statistical correction for the number of people who are unlikely to make it into the survey.

Under this methodology, we arrive at the 11 million figure. But population size doesn't say much about who these people are. So Passel digs further.

He assigns statistical probabilities to the BLS data set to indicate who among the survey respondents might be illegal (the data does not include personal identifiers). It then becomes a process of logical elimination to find which of the 40 million immigrants in the BLS data are also here illegally.

Passel offers some examples. "We say, this person is a veteran, this person served in the armed forces, so we're going to say they are legal," he says. "This person is a certified public accountant — we're going to say they are legal.... This person is not getting welfare, this person works, this person is a construction worker — so they may be legal or illegal."

Through this roundabout process, we've come to our best guess at the makeup of the undocumented-immigrant population. If a pathway to legalization is affirmed, this picture will only become more clear.

Through his research, here's what we know about the 11 million.

They've come here to settle down.

"The unauthorized immigrant population is, to a degree that I think that is largely unappreciated, a group of families with children," Passel says. Twenty-one percent of nonimmigrant households are couples with children. In other words, nuclear families. In households of illegal immigrants, that number jumps to 47 percent, according to 2008 data.

"More than half of the adult men are in families, are married, or have a partner," he says. "And most of them, 80 percent of that half, have children here. The women represent about 40 percent of the adults, and almost all of them are not here by themselves." Part of this is due to difference of ages in the sample. The undocumented families are younger, and therefore more likely to have children. Nonetheless, the data is indicative of people who have come here to raise a family.

They've been here for a while.

According to 2010 Pew data, 63 percent of unauthorized adults had been in the country 10 years or more.

They're mainly from Mexico.

"Any place that sends us immigrants, we have some unauthorized immigrants from," Passel says. But around 55 to 60 percent are from Mexico, "which translates to over 6 million people. There is no other country that has sent as many as 500,000."

Twenty-one percent fall below the poverty line.

The number of new illegal immigrants has declined in recent years.

The number of undocumented workers peaked in 2007 at 12 million and then declined to a steady 11 million in the following years. "From 1990 to 2007, there were a lot more coming than leaving, so the numbers were growing steadily," Passel says. "With the onset of the recession, the numbers of people coming plummeted. There some evidence that the numbers leaving increased, but the main reason the growth stopped is that the people stopped coming."

The decline in the number of illegal immigrants is influenced by the recession, but also by tougher border practices.

"We have data that says its harder to get in, its harder to sneak in," he says. "We have data that shows the cost of hiring a smuggler has gone up, we know that the enforcement practices have pushed a lot of people who were trying to sneak into more remote areas so it is more dangerous physically.... But then when you look at the U.S. economy, it might be hard to find a job. You put all that together and it's not all that surprising that many, many fewer people are trying to come into the U.S."

If a pathway to legalization is made, we'll learn a lot more about this group.

"To some degree, a lot of the information we have on their characteristics is speculative," Passel says, because so much of the data is based on probability, and not an actual survey of illegal immigrants. "We're inferring who the people are who are undocumented, and that we are not actually asking people whether they are unauthorized or not. And some of those inferences that we are making are coming from surveys that were conducted 25 years ago when we had legalization [under President Reagan]. So if we go forward with some sort of legalization, we'll get a clearer picture of who they are."

But more than who they are, we can find out what they believe about their futures in the United States, and how they hope to shape the country.

"One of the things the Pew Research Center does is try to understand what motivates people, what their opinions are," he says. "Those are things that if we go forward with this and have an identifiable group of people who are former unauthorized immigrants, we can learn something about how they came, why they came."

They've been here for a while.

According to 2010 Pew data, 63 percent of unauthorized adults had been in the country 10 years or more.

They're mainly from Mexico.

"Any place that sends us immigrants, we have some unauthorized immigrants from," Passel says. But around 55 to 60 percent are from Mexico, "which translates to over 6 million people. There is no other country that has sent as many as 500,000."

The number of new illegal immigrants has declined in recent years.

The number of undocumented workers peaked in 2007 at 12 million and then declined to a steady 11 million in the following years. "From 1990 to 2007, there were a lot more coming than leaving, so the numbers were growing steadily," Passel says. "With the onset of the recession, the numbers of people coming plummeted. There some evidence that the numbers leaving increased, but the main reason the growth stopped is that the people stopped coming."

The decline in the number of illegal immigrants is influenced by the recession, but also by tougher border practices.

"We have data that says its harder to get in, its harder to sneak in," he says. "We have data that shows the cost of hiring a smuggler has gone up, we know that the enforcement practices have pushed a lot of people who were trying to sneak into more remote areas so it is more dangerous physically.... But then when you look at the U.S. economy, it might be hard to find a job. You put all that together and it's not all that surprising that many, many fewer people are trying to come into the U.S."

If a pathway to legalization is made, we'll learn a lot more about this group.

"To some degree, a lot of the information we have on their characteristics is speculative," Passel says, because so much of the data is based on probability, and not an actual survey of illegal immigrants. "We're inferring who the people are who are undocumented, and that we are not actually asking people whether they are unauthorized or not. And some of those inferences that we are making are coming from surveys that were conducted 25 years ago when we had legalization [under President Reagan]. So if we go forward with some sort of legalization, we'll get a clearer picture of who they are."

But more than who they are, we can find out what they believe about their futures in the United States, and how they hope to shape the country.

"One of the things the Pew Research Center does is try to understand what motivates people, what their opinions are," he says. "Those are things that if we go forward with this and have an identifiable group of people who are former unauthorized immigrants, we can learn something about how they came, why they came."

This article is from the archive of our partner National Journal.