Public speaking: repeating a message does not prove it
When presenting a project, the advice to repeat the central message seems reasonable. The management question is more precise: how can a proposal be made memorable without its familiarity being mistaken for evidence?
What the literature establishes
Lynn Hasher, David Goldstein and Thomas Toppino (1977, Journal of Verbal Learning and Verbal Behavior) showed that repeated statements were judged truer than new statements. Their experiment examined validity judgements, not the quality of professional presentations. It nevertheless establishes an important distinction: repetition can change perceived truth without providing additional evidence.
Why knowledge is not always enough
Lisa K. Fazio, Nadia M. Brashier, B. Keith Payne and Elizabeth J. Marsh (2015, Journal of Experimental Psychology: General) observed that this effect could occur even when participants had the knowledge needed to recognise a false statement. Their findings are consistent with a fluency mechanism: a previously encountered statement becomes easier to process, and that ease can contribute to truth judgements. Having relevant knowledge therefore does not guarantee that it will be used when making a judgement.
The premature conclusion
One might conclude that effective public speaking requires frequent repetition, or alternatively that repetition should be avoided altogether. These studies justify neither general prescription. The useful distinction is between restating a proposal and restating what makes it verifiable. (our executive and employee training programmes)
What the evidence does not establish
These experiments use statements and truth ratings under controlled conditions; they do not reproduce an investment decision or a scientific project review. They cannot establish an optimal number of repetitions or predict the size of the effect in an expert committee. In practice, assessing only a speaker’s clarity or persuasiveness does not test whether the audience can better distinguish established findings from hypotheses.
A practical check in Bâle
In a workshop within SHR’s “Public Speaking & impact” programme in Basel, participants could work on a presentation about industrial transfer or supply continuity connecting pharma, life sciences, Rhine logistics and international R&D. For each central proposal repeated in the conclusion, the speaker identifies the available evidence and its limitation, after which each participant separately recalls the proposal, its source and a remaining uncertainty. The measure is the proportion of responses correctly identifying all three elements, checked against a rubric prepared from the reference dossier. Comparing this indicator between an initial presentation and its revised version provides a learning benchmark, without being sufficient to attribute the change to training alone. To go further: explore the Public Speaking & Impact training in Basel, or browse our executive and employee training programmes in Switzerland.
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