The generality of the ratio-bias phenomenon

A well-substantiated, surprising finding is that people judge the occurence of an event of low probability as less likely when its probability is represented by a ratio of small numbers (e.g., 1 in 20) than of larger (e.g., 10 in 200) numbers. The results of three experiments demonstrated that this phenomenon is broadly general and occurs as readily in pre- as in postoutcome judgments. These results support an interpretation in terms of subjective probability, as suggested by the principles of cognitive-experiential self theory, but not as an interpretation in terms of imagining couter-factual alternatives, as proposed by norm theory.