Yes, I have in fact heard that term, which is exactly why I know that anecdotal evidence is not valid.

What does invalid evidence add to the discussion, exactly?

There are people in this thread who are arguing for legislation restricting ownership of pitbulls. We are in the court of public opinion, which may be less formal than the supreme court, but still has the capacity to influence public policy. So it seems reasonable to apply a very basic standard of evidence, above that of stuff that random people claim happen to their friend's roommate.