Although the estimated number of unauthorized immigrants into the United States dropped off after 2007, researchers think that number may be on the rise again.
After estimating a peak of 12.2 million unauthorized immigrants in the country in 2007, the Pew Research Center estimated that number dropped to 11.3 million by 2009, and now estimates 11.7 million unauthorized immigrants are in the country.
The problem is, it's unclear if that's actually a rise in unauthorized immigrants, since it falls within the large margin of error.
You can probably imagine why it would be difficult to estimate how many undocumented immigrants there are.
Pew concedes that the new estimate is "in a statistical sense is no different from the 2009 estimate," but does cite other indications that there was an increase.
Interestingly, although the number of Mexican unauthorized immigrants appears to have decreased, the number of non-Mexican unauthorized immigrants appears to have increased, according to Pew's research.
In fact, Pew estimated last year that more Mexican immigrants crossed the border back into Mexico than came into the United States.
However, it's still not clear which way unauthorized immigrants are flowing.