THE SUBJECTIVE BELIEFS UNDERLYING PROBABILITY OVERESTIMATION

Teigen (1974a, 1974b, 1983) observed that the numerical probabilities assigned to a set of exhaustive and mutually exclusive events frequent ly exceed one. Three experiments were performed to examine why these i nflated numerical probability judgments form and what they reflect abo ut people's subjective beliefs. Some work suggests that numerical prob ability overestimations stem from a fundamental misunderstanding of th e rules of probability calculation. Our findings, though, indicate tha t biased hypothesis testing processes operate that contribute to the s ubjective overestimation of the likelihood of a hypothetical event. Pe ople tend to perceive events to be more plausible than is possible bec ause of confirmatory processes characterizing the selective testing of a hypothesis. Our findings indicate that these processes may lead to the unwarranted disconfirmation of a focal hypothesis when the evidenc e for all of the alternatives is weak. (C) 1997 Academic Press.