Public speaking: does acknowledging uncertainty undermine trust?
Before an executive committee, a range may seem less persuasive than a single figure. The managerial question is specific: how can a speaker present an uncertain estimate without unnecessarily weakening trust or implying certainty that does not exist?
What the literature establishes
Anne Marthe van der Bles, Sander van der Linden, Alexandra L. J. Freeman and David J. Spiegelhalter (2020, Proceedings of the National Academy of Sciences) experimentally examined how communicating uncertainty affects trust in facts, numbers and their sources. Expressing numerical uncertainty as an interval generally entails only a small trust penalty, if any. In their experiments, verbal expressions of uncertainty can be more detrimental than numerical intervals: acknowledging a limitation does not therefore automatically discredit a speaker.
What “uncertain” actually means
Anne Marthe van der Bles, Sander van der Linden, Alexandra L. J. Freeman, James Mitchell, Ana B. Galvao, Lisa Zaval and David J. Spiegelhalter (2019, Royal Society Open Science) distinguish, among other things, uncertainty about an estimate from uncertainty about the quality of the knowledge underpinning it. A range describes the former but does not necessarily convey the latter. The speaker therefore needs to clarify whether the qualification concerns the stated value, the available data or the assumptions used.
The premature conclusion
One might conclude that simply adding a range makes a presentation more credible. These studies demonstrate neither an automatic gain in credibility nor a systematic improvement in decisions. An unjustified interval can also lend an appearance of rigour to a fragile forecast. (our executive and employee training programmes)
What the evidence cannot promise
The cited experiments do not directly test a presentation to a banking committee or the management of a family business. They cannot isolate the effects of hierarchy, commercial interests or a challenging discussion in Italian. Above all, maintaining trust does not prove that the audience understood the uncertainty: these two outcomes need to be measured separately.
A practical check in Lugano
Within SHR’s “Public Speaking & impact” programme, an exercise in Lugano could focus on a margin forecast in banking, sales in fashion, delivery in trading or investment in an Italian-speaking family SME. Randomly assign participants to two Italian versions of the same presentation, equal in length: one gives only the central estimate, while the other adds a justified range and the main limitation of the data. Afterwards, collect individual trust ratings on the same scale and written accounts of what remains uncertain, without discussion between participants. Comparing trust and the proportion of responses correctly identifying the stated limitation provides a local check without turning the result into a universal rule. To go further: explore the Public Speaking & Impact training in Lugano, or browse our executive and employee training programmes in Switzerland.
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