Do claims about certainty make estimates less certain?

Area of Science:

• Cognitive Psychology
• Linguistics
• Decision Science

Background:

• Verbal probability expressions often place "certainty" at the highest level, implying probabilities near 1.
• Few studies have compared explicit certainty claims with plain, unqualified statements.

Purpose of the Study:

• To investigate how explicit claims of certainty affect perceptions of credibility, precision, and evidential support.
• To compare explicit certainty statements with plain, unmarked declarative statements.

Main Methods:

• Nine studies involving 2784 participants were conducted.
• Participants evaluated statements with and without explicit certainty markers on scales of credibility, precision, and evidential basis.

Main Results:

• Statements claiming certainty were often perceived as less trustworthy, reliable, and held with lower confidence than unmarked statements.
• Certainty statements were found to be more ambiguous, potentially indicating undefined upper bounds and affecting interpretations in risky choice scenarios.
• Impersonal certainty ("it is certain") was perceived as more accurate than personal certainty ("I am certain"), particularly for future predictions.

Conclusions:

• Explicit claims of certainty can undermine credibility and precision, contrary to common assumptions.
• Omitting certainty claims may enhance the perceived consensus of estimates.
• Effective communication of certainty might be achieved by avoiding explicit mentions of certainty.