ABSTRACT
When assessing the likelihood of an event, human judgment is often inconsistent with the rules inherent in standard probability theory. For example, the judged probability of an event can be heavily influenced by the alternatives that are explicitly presented. Tversky and Koehler (1994) attempted to account for this phenomenon by arguing that probability judgments are made by comparing the amount of cognitive support one holds in favour of the event in question relative to all other possibilities. They suggested that different descriptions of the same event elicit different amounts of support resulting in different probability ratings. In addition to the role played by explicitly considered alternatives, the present paper suggests that people are also sensitive to the influence of alternatives that are not considered explicitly. We present the term ‘implied numerosity’ in an attempt to indicate that probability ratings are influenced by a general impression of the number of potential alternatives that exist Systematic differences in probability estimations may result from systematic changes in the perceived size of the category being evaluated.
