The Illusion of Lie Effect: The Suspicious Fluency of Round Numbers

Round numbers have been defined as multiples of the powers of the base (e.g., multiples of 10 in the commonly used base 10 number system, see Dehaene and Mehler 1992) or as numbers whose factorial content includes 2, 5, or 10 (Sigurd 1988). Intuitively, most individuals would likely agree that 5, 40, 125, or 3740 are “rounder” numbers than 6, 41, 128, or 3739. Individuals often employ such numbers “to indicate not only the quantity represented by the number itself, but also quantities that could be more precisely described by numbers close in value to the reference number” (Jansen and Pollmann 2001, p. 190). Round numbers are more common than other numbers in communication contexts, conducive to individuals’ greater liking thereof. They are often used as milestones and granted special meaning even when none is rationally warranted (e.g., rational investors prefer round numbers for the prices of the stocks they buy–Bradley et al. 2004, Kandel, Sarig, and Wohl 2001). The fondness for round numbers is not indiscriminate. It seems to largely apply to categories that involve metrics associated with commonplace categories or phenomena. For categories involving unfamiliar natural or random phenomena, a paradoxically opposite effect occurs whereby round numbers are suspiciously fluent and best avoided. This comes from the perception that, in unfamiliar contexts that feature randomness, the occurrence of an event that can be precisely quantified via something as common as a round number is surprising and considered highly unlikely. Anecdotal evidence includes the scientific expedition to measure Mt. Everest that came up with a perfect 29,000 ft. altitude but arbitrarily added another 2 feet before making it public because it was assumed that the perfectly round measurement would be disbelieved. Research on lottery number picks has found that out of the six least commonly played numbers in Canada’s 6/49 Lotto game a full half are round numbers (Stern and Cover 1989). Round numbers thus are preferred when describing the magnitudes of known objects and situations (i.e., the principle of favorite quantities –see Jansen and Pollman 2001), but also shunned and distrusted when paired with unfamiliar phenomena and quantities. In the latter instance, we face the unusual case of enhanced levels of fluency and familiarity which, instead of increasing liking and creating approach, raise suspicion and produce avoidance via an illusion of lie effect.