Racial segregation has been declining since the 1970s but it clearly exists.

For example, the average black person lives in a neighborhood that is 45 percent black. Without segregation, his neighborhood would be only 13 percent black.

The slow decline of segregation was revealed in 2010 census data and analysis by professors at Brown and Florida State University.

John Logan and Brian Stults created a dissimilarity index, which identifies the percentage of one group that would have to move to a different neighborhood to eliminate segregation -- think busing.

A score above 60 on the dissimilarity index is considered very high segregation. 22 metropolitan areas crossed this threshold.