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In judging posterior probabilities, people often answer with the inverse conditional probability-a tendency named the inverse fallacy. Participants (N = 45) were given a series of probability problems that entailed estimating both p(H | D) and p(,H | D). The findings revealed that deviations of participants' estimates from Bayesian calculations and from the additivity principle could be predicted by the corresponding deviations of the inverse probabilities from these relevant normative benchmarks. Methodological and theoretical implications of the distinction between inverse fallacy and base-rate neglect and the generalization of the study of additivity to conditional probabilities are discussed.

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Decision framing concerns how individuals build internal representations of problems and how these determine the choices that they make. Research in this area has been dominated by studies of the framing effect, showing reversals in preference associated with the form in which a decision problem is presented. While there are studies that fail to reveal this effect, there is at present no theory that can explain why and when the effect occurs. The purpose of this article is to present a selective review of research and use this to argue for a new framework for considering decision framing, to interpret past studies, and to set an agenda for future research. A simple informationprocessing model is developed. The model provides the basis for arguing that previous research has taken too narrow a view of how decision problems are internally represented and how these representations are transformed into choice behaviour. In addition, the model is used to highlight the importance of decision content and context.

When a statement about the occurrence of a medical condition is qualified by an expression of probability, such as the word possible, listeners interpret the probability of the condition as being higher the more severe the condition. This severity bias can have serious consequences for the well-being of patients. We argue that the bias is due to a misconception of the pragmatic function served by the expression of probability. The more severe the condition, the greater the chance that the listener construes the expression as a politeness marker rather than as an uncertainty marker. When this misconception does not occur, neither should the severity bias. An analysis of interpretations of probability expressions using a membership-function approach validates this account. We discuss the consequences of this bias for the communication of risk within and outside the medical domain.

Two experiments examined the relationships between the knowledge that another person has won in a gamble, the illusion of control and risk taking. Participants played a computer-simulated French roulette game individually. Before playing, some participants learnt that another person won a large amount of money. Results from a first experiment (n = 24) validated a causal model where the knowledge of another person's win increased the illusion of control, measured with betting times, expectancy and self-reports on scales, which in turn encourages risk taking. In the second experiment (n = 36), some participants were told the previous player acknowledged the win to be fortuitous. The suppression of the belief that the previous winner had himself exerted control over the outcome resulted in lower rates of risk-taking behaviors. This suggests that it was not the knowledge of another person's win in itself that increased risk taking, but rather, the belief that the other person had some control over the gamble's outcome. Theoretical implications for the study of social mechanisms involved in gambling behavior are discussed.

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This research focuses on what determines speakers' choice of positive and negative probability phrases (e.g., "a chance" vs. "not certain") in a legal context. We argue that choice of phrase to describe an event's probability of occurrence can be determined by the contrast between its current p value and an earlier p value, and not by that current value alone. Three experiments were conducted describing scenarios where profilers communicated a suspect's probability of guilt to the police. In the first study, a probability estimate is revised upwards or downwards. In the second one, the probability estimate of a speaker is higher or lower than that given by a previous speaker. In both cases, participants expected upward trends to lead to positive phrases, whereas downward trends were associated with negative phrases. In a third study, participants had to select probability phrases to characterize two different suspects. No contrast effects were found. We conclude that verbal probability directionality has primarily an argumentative function, where positive phrases are selected when probabilities are contrasted with smaller p values, and negative when contrasted with higher p values.