https://www.imf.org/external/pubs/ft...15/sdn1513.pdf

"First, we show why policymakers need to focus on the poor and the middle class. Earlier IMF work
has shown that income inequality matters for growth and its sustainability. Our analysis suggests
that the income distribution itself matters for growth as well. Specifically, if the income share of the
top 20 percent (the rich) increases, then GDP growth actually declines over the medium term,
suggesting that the benefits do not trickle down. In contrast, an increase in the income share of the
bottom 20 percent (the poor) is associated with higher GDP growth. The poor and the middle class
matter the most for growth via a number of interrelated economic, social, and political channels."

Also:

http://www.bbc.com/news/blogs-magazine-monitor-31847943
http://www.oecd.org/social/income-di...n-database.htm