A new study says the wealth gap between African Americans and whites in the United States has nearly tripled over the last quarter century. Researchers at Brandeis University who tracked households over time say the median wealth of white families grew to become more than $236,000 higher than that of black families by 2009. They cited homeownership as a top cause and urged policies to ensure “that the legacy of residential segregation no longer confers greater wealth opportunities to white homeowners than it does to black homeowners.”