...The top 20% of earners give about 1.3% of their income to charity. But the lowest 20% of earners give almost three times more -- 3.2% of their income. That's a huge gulf.

http://www.futurefundraisingnow.com/future-fundraising/2013/05/why-the-rich-give-proportionally-less-and-what-to-do-about-it.html