As a researcher, I'm interested in mechanisms ... do you have a guess for why reduced stuttering results in increased confidence? Is stuttering severity more salient to 'confidence' than stuttering frequency? Are they equally salient? I agree that anxiety is not the reverse of confidence. Confidence is a construct -- there are lots of "things" in confidence. For some people anxiety (or lack thereof) might be a part of what defines "confidence" but not necessarily everyone.