I'm glad to see that this one has some mathemagics behind it. IMO, all graphs should have their source numbers right there like this one does.
A few things I'd like to note:
1- If you make less than $75,000, you're not included.
2- If you donate less than $xx, (varies by state) you don't need to itemize your charitable deductions. So you're not included either.
3- There is no need to go through all this "Having rank", "Giving rank", etc. This should be as simple as Miles per Gallon. Take the miles, divide by gallons. In this case, if you want to know donated dollar per income dollar, just divide it out. It moves things around a bit.
As a sidenote, I've been doing some research on charitable organizations themselves (shut up, you're dorky too. Look at the site we're at

). I am shocked at how many are a straight up con. Take "A Childs Wish" for example. Sounds legit, but check it out:
http://www.give.org/reports/care2_dyn.asp?125 There's a whole pile of them at:
http://www.give.org/reports/index.asp