The Generality of the Ratio-Bias Phenomenon

A well-substantiated, surprising finding is that people judge the occurrence of an event of low probability as less likely when its probability is represented by a ratio of smaller (e.g., I in 20) than of larger (e.g., 10 in 200) numbers. The results of three experiments demonstrated that the phenomenon is broadly general and occurs as readily in pre-as in post outcome judgments. These results support an interpretation in terms of subjective probability, as suggested by the principles of cognitive-experiential self theory, but not an interpretation in terms of imagining counter-factual alternatives, as proposed by norm theory.