According to census data, Los Angeles has seen its Black population shrink from around 18 percent in 1970 to 9.9 percent four years ago.
http://www.lasentinel.net/index.php?option=com_content&view=article&id=3131:census-results-reveal-blacks-leaving-large-cities&catid=70&Itemid=160
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BTW, this is substantial!
Apples and oranges. Decreasing percentage does not equate to leaving. The hispanic numbers have just gone up.