The American Medical Association copyrighted it. I didn't know factual information can't be copyrighted. The "copyright" text on their website is rubbish then. Learn something new everyday. Thanks!

I think simply a collection of facts can't be copyrighted. It must have some kind of creative added value for copyright to be applicable, like an encyclopedia presenting these facts may be would be an example.

And yeah, it's not uncommon for some to slap "copyrighted" on something where it's not applicable.