It's funny how some untruths become widely accepted as true. The oft-quoted statistic "Only 7% of our communication is conveyed by words (38% tone of voice, 55% body language)" appears in many textbooks, and is quoted by speakers and "communication experts" as though it were not only true, but proven.
In fact, it is a huge misinterpretation of an experiment carried out many years ago by Albert Mehrabian, when he studied feelings and attitudes when people make a judgement about liking or disliking someone. Mehrabian himself has stated that he never intended his results to be applied to conversation (and definitely not to public speaking).
Yet the myth has been propagated far and wide, by people who should have checked what Mehrabian really did. (I'm sure you were never fooled, of course).
Alas, I have debated many times with people who believe that the 7-38-55 rule can be applied to almost any communication, completely ignoring the evidence of their senses, let alone the origin of the figures. I have had several on-stage debates with NLP practitioners, who have professed "it must be true - it's in our textbooks".
Of course, tone of voice and body language are important, as is congruence between verbal and non-verbal communication. But please, let's not propagate this 7% myth any further