The share of Americans who identify themselves as multiracial has shrunk this decade, a trend that defies expectations in an increasingly diverse nation.Less than 2 percent of the U.S. population checked off more than one race in the Census Bureau’s 2005 American Community Survey (ACS). In two Census surveys in 2000, more than 2 percent did.”There’s no overall explanation” for the drop, says Reynolds Farley, research scientist at the University of Michigan’s Institute for Social Research who analyzed the trend.

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