> Is there evidence that saying 'umm' and 'ahh' reduces your ability to communicate effectively? Why are they bad?

Hmm I can't find any good research though at least anecdotally it makes it a lot hard for me to pay attention. Take Paul Graham for instance. Smart guy, great speaker but his frequent "umms" ended up taking me out of his talk and then I couldn't concentrate on anything but his "umms". I love reading his essays but I find it hard to concentrate on his speaking.

Granted I don't know if that says something negative about my ability to concentrate, about Paul's speaking ability, or both and it's anecdotal so no idea if my experience is common.