How much did the U.S. foreign-born population grow from 2009 to 2010? According to the Census Bureau’s American Community Survey, the number grew by 1.5 million, or 4%. But a new Pew Hispanic Center analysis concludes that the growth was markedly lower.

The Pew Hispanic analysis states that the foreign-born population grew by 616,000, or 1.5%, from 2009 to 2010. Both the ACS and Pew Hispanic estimates agree that the foreign-born population total was 39.9 million in 2010. The reason for the difference in their estimates of population growth is that the Pew Hispanic Center analysis includes a higher estimate of the foreign-born population in 2009 (39.3 million) compared with the total reported by the ACS (38.5 million).

The Pew Hispanic Center revision was undertaken to account for changes between 2009 and 2010 in the Census Bureau’s assumptions about population composition that underlie the reported ACS estimates. The 2010 ACS is based on the latest information from the 2010 Census; the 2009 ACS is based on updates to the 2000 Decennial Census. The difference in method from one year to the next affected the magnitude of the estimates of change in the foreign-born population. See the full report for more information on how the Pew Hispanic Center calculated a revised estimate for 2009 that is consistent with the 2010 data.