Anecdotal evidence proves nothing.
Well, perhaps we're being too hasty. If we assume that the anecdotal evidence we are hearing is true, we could use it to disprove a universal claim. For example, if someone claims that all midgets are blind, you could disprove the claim by reporting that you have a cousin who is a sighted midget. If we assume that you are speaking the truth, then it cannot be true that all midgets are blind. What we could not do is extrapolate from the happy case of your cousin to a statement about the sightedness of midgets in general.