I have abused this rule in almost all my talks! So I am guilty as charged.
You may have heard people saying what you say only contributes to a small percentage of the impact of your communication and that how a person says what they say has a far greater impact. The rule, which is and has been promoted by many speakers and trainers states that 55% of the meaning of communication is body language, 38% is in tonality, and 7% rests in the words themselves.
Where did this rule come from?
Professor Albert Mehrabian Ph.D., of the University of California, Los Angles (UCLA), is credited as the originator of the 55%, 38%, 7% Rule. He and his colleagues conducted two studies on communication patterns and published the studies in professional journals in 1967.
Mehrabian later discussed the results of the studies in two books in the early 1970s. The results of the studies were widely circulated in the press, in abbreviated form, leading to a misunderstanding of the original research and inaccurate generalizations of the conclusions.
Below, an article about the research conducted by Albert Mehrabian.
A Linear Model for the Inference of Attitudes from Multichannel Communications
Mehrabian and Wiener (1967) and M and Ferris (1967) investigated the combined effects of consistent or inconsistent verbal-vocal communications and consistent and inconsistent facial-vocal communications of attitude respectively. Both studies involved nine sets of communication stimuli.
In the M W study, verbal-vocal communications were prepared so that three degrees of positive verbal content were associated with three degrees of vocally expressed attitude. Having been judged for amount of liking conveyed, the words honey, thanks and dear were selected as instances of positive contents ( the judgments of these words had comparable mean values and standard deviations ). Similarly, the words maybe, really and oh were selected as comparable instances of neutral contents; and the words don’t, brute and terrible were selected as comparable instances of negative contents.
Two female speakers were employed to read each of the nine selected words in positive, neutral and negative vocal expressions. For these three conditions, respectively, the speakers spoke the words, regardless of content to convey, liking, high evaluation, or preference; a neutral attitude, that is, neither liking nor disliking; and an attitude of dislike, low evaluation, or lack of preference towards the target person. All possible combinations of two speaker conditions, three vocal conditions, three content conditions, and three instances of each content condition were recorded on tape.
To obtain the independent effects of the vocal and content components of these recordings, and to relate these to the effects of the total vocal content messages, Mehrabian and Wiener (1967) had three different groups of subjects listen to these recorded messages. One group was asked to judge the degree of liking conveyed by each message, relying only on the meanings of the words used and not on the vocal expression. The second group was asked to judge the degree of liking relying only on the vocal component and not on the meanings of the words used. Finally, the third group formed their judgments of liking on the basis of all the information combined in each message.
The results of the study showed that the vocal component in the various messages primarily determined the subjects’ judgments of affect from the total messages (content and vocal components combined), and that the content component of inconsistent messages had a negligible contribution to the affect inferred from such statements.
As you will realize now, the rule of 55%, 38%, 7% is not correct and only applicable in situations where messages are incongruent.
Mehrabian actually stated (Anchor Point, 1994) that he never intended his results to be applied to normal conversation (and assumedly not to public speaking either). He only wanted to help his readers resolve incongruent messages regarding liking and disliking. Thus, his research has useful, yet limited applications, which have been blown out of proportion.