I'd be interested in knowing any statistics on the matter. Do you know of any? To me, the idea that stuttering is caused by nerves is a myth and misconception about what stuttering is. Many non-stutterers stutter in nervous situations themselves, so the fact that nerves can lead to less ability to control speech would also be seen in the same proportion of stutterers. I think, in some situations, this could lead to misdiagnosis of what's going on when stutterers show worse fluency when nervous. As in, it might just be a natural disfluency on top of/exacerbating the stutter, but the actual level to which the natural stutter on its own (whatever mechanism or thing that is inside of us) is affecting fluency is the same. But everyone stutters differently, and certainly people see it show in different situations, and for sure many people find it worse when nervous. I am undoubtedly worse on the phone. I theorize it is because of the lack of reciprocity in face-to-face interactions. There is not that smooth sense of when the other person wants to say something, looking into people's eyes, reading their face, etc. It is pure speech and much more of a battle for me. Perhaps one thing contributing to my opinion is I don't get nervous very much or often. I long since stopped caring about what other people thought of my speech.