It goes without saying that the United States is a nation of immigrants. With the exception of indigenous native populations, most of us can claim an ancestry (distant or otherwise) derived from the passage of one group of people via land, ocean, or (in recent cases) air. Even so, every stage of our nation’s history has been fraught with difficult, and often controversial, decisions about immigration policy (Who should be admitted? How many? From where?) As this is the start of an election year, immigration policy is again in the news, but much of the essential information about numbers and types of immigrants is either overlooked or oversimplified. Here’s a primer on some of the latest numbers available, along with links for further research to help your students be informed citizens.

U.S. citizens overestimate size of immigrant population

Ipsos MORI, a British market research firm, conducted a recent demographic study in which they polled residents of various countries to self-reflect about their demographics through a series of questions. In one question, participants were asked what percentage of their country’s population are immigrants. Nearly every country that participated overestimated the percentage of recent immigrants. The United States was no exception — on average most polled believed that immigrants comprise 33% of the U.S. population, when in reality, immigrants make up 14%.

Numbers and Classifications of U.S. immigrants

At times, immigration can be distilled into a binary of ‘documented’ versus ‘undocumented,’ though the truth is more complicated. The designations that separate recent immigrants are critical to understanding the data. Even the category of ‘undocumented’ can be misleading. Those who are undocumented are not always ‘illegal’ immigrants. The Department of Homeland Security (DHS) recognizes the following designations as legal immigrants: lawful permanent residents, immigrant orphans, unaccompanied minors, refugee arrivals, and asylum seekers. (2013 DHS Yearbook of Immigrant Statistics).

In total, there were 1,130,994 legal immigrants to the U.S in 2013 (the most recent year that data is available). That number, however, is somewhat misleading, since nearly half of the “lawful permanent residents” had already been in the country prior to 2013, but their status had changed that year. Additionally, about 40 percent of asylum seekers (those designated as “defensive”) flee to the U.S. in one year and apply for asylum later, risking being counted twice. So, the total number of immigrants entering the U.S. legally in 2013 with the intention to stay was actually 590,259.

Trends in Illegal Immigration

According to the Pew Research Center, the number of unauthorized immigrants to the U.S. has stabilized in recent years after decades of rapid growth. The number of unauthorized immigrants living in the U.S. reached a high of 12.2 million in 2007. In 2014, that number was estimated at 11.3 million (about 3.5% of the U.S. population). In the years following the Great Recession (2009-2014), about 1 million Mexicans left the U.S. to return to Mexico.

So how is it that we can collect so much data, and still end up with such wide margins between the conclusions we draw? Because immigration reporting is a massive undertaking – and it is replete with redundancies and difficulties in segregating populations evenly and distinctly from each other. Even in our data-heavy world, measuring people and their movements is a feat. There are few consistent models — even between countries that do conduct censuses — for how to collect the data, and when, and with what tools.

But that doesn’t mean we should shy away from working with the numbers. When we look carefully at statistics, they can give us greater insight into our own misunderstandings, ourselves, and ever shifting human patterns.