I'd recommend http://creativecommons.org/licenses/by-nd/3.0/nz/ . The "no derivative works" would, I presume, protect the site's authors against misquotation or falsification of their views through dishonest paraphrase.
The graph in question is here. (Security word: "AUTHORITYS". Is someone around here trying to discourage good spelling and grammar?)
You think that's bad? I have it on good authority that fifty percent - that is, one in every two - New Zealand school children are of below average intelligence!