I work in IT for marketing company in Akron Ohio that works with a lot of non-profit & charity companies along side our commercial clients so I see the how their programs operate, translate their business rules into code, and aid in the running & writing of their SRS reports that we send to them daily.
Average Response Rate: 9.6%...and that's not broken out by political party...that's across the board.
Is that good enough? Does first hand tangible knowledge count as proof?
I have a friend who works for a tax firm who told me that some people who make 20mil+ a year get away with only paying 3% in taxes...but somehow they're just so broke, they can't help anyone. I pay about 30% in taxes...then donate an addition grand to charity every year....so they have no excuse.