Stocks Widen Gap Between Rich and the Rest: Study

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At the early stages of the recovery, the wealthy rebounded while the rest floundered. One study found that in 2010, 93 percent of the economic gains in the United States went to the top one percent of earners.

Some chalked this up to political policy. Others blamed the Fed, or tax rates on the wealthy, or a rigged financial system.

But there's a more simple answer: stock investments.

A new research paper from the Pew Research Center, using census data, found that from 2009 to 20911, the top 7 percent of Americans by wealth owned 63 percent of the nation's total wealth – up from 56 percent in 2009. The mean wealth of the top 7 percent (about 8 million households) jumped to $3.17 million from $2.48 million over the two years.

(Read more: Booming Market Adds 300,000 Millionaires)

In contrast, the mean wealth of the bottom 93 percent fell to $133,817 from $139,896.

The reason, according to the paper, is that stocks recovered and housing didn't. The wealthy have their wealth concentrated in stocks, while the less affluent have their wealth concentrated in their homes.

The study said that 65 percent of the wealth held by households worth $500,000 or more comes from financial holdings, such as stocks, bonds and 401(k) accounts. Only 17 percent comes from their homes. Among those with less than $500,000, only 33 percent of the wealth comes from financial assets, with 50 percent coming from their homes.

Also, fewer of the less wealthy households held stocks in 2009 than in 2007, so they missed out on the rally.

(Read more: Has Wealth Inequality Sparked the Fed's Interest?)

"The different performance of financial asset and housing markets from 2009 to 2011 explains virtually all of the variances in the trajectories of wealth holdings among affluent and less affluent households during this period," the report stated.

Of course, housing prices have since started climbing back. The data for 2012 and 2013 could show more evenly distributed wealth gains in the U.S. and perhaps a stabilizing or slight decline in inequality.

But for now the lesson is clear: the stock-wealthy did better than the house-wealthy.