Comparing two recent five-year blocks, the report finds that not only has the number of Mexicans immigrating to the U.S. declined by 50 percent (from 3 million to about 1.4 million), the number of Mexicans going the other way back home has doubled.

Seven hundred thousand Mexicans in the U.S. moved back between 1995 and 2000. But that number increased to 1.4 million between 2005 and 2010.

This has several explanations. The U.S. economy is weaker. On the other hand, Mexico's economy is strengthening. Its GDP per capita is 15,000 dollars - about a third that of America's. Some of Mexico's competitiveness is due to NAFTA - the North American Free Trade Agreement. Because it avoids U.S. tariffs, its exports work out to be cheaper than China's. Last year, Mexico did 400 billion dollars worth of business with the U.S. That's more than Argentina and Brazil combined.