Latest results: Wolf, Rieger & Knauff 2012

Ann Wolf, Susann Rieger and Markus Knauff have found that people’s belief in a conditional such as ‘if Chris goes to work then he will take the car’ dropped when it was uttered by an individual with a ‘low-trustworthy’ occupation, e.g. a used-car salesman or a real-estate agent compared to one with a ‘high-trustworthy’ occupation, e.g. a pilot or a firefighter, when they are given tasks which required them to revise their beliefs, e.g., ‘if Chris goes to work then he will take the car. Chris does not take the car. Chris goes to work’. Their results are published in their paper The effects of source trustworthiness and inference type on human belief revision  in  Thinking & Reasoning (2012, 18, 417-440). They summarise their results in their abstract there:

“We investigated whether people revise their beliefs as a function of inference trustworthiness. By doing so we aimed to find out if belief revision is better explained by mental model theory (Johnson-Laird & Byrne, 2002) or by a conditional probability view (Evans, Handley, & Over, 2003; Oaksford & Chater, 2001). We used modified modus ponens (MP) and modus tollens (MT) problems in which the first two premises were uttered by persons with varying degrees of trustworthiness. A third statement was presented as a fact and established inconsistency in the set of propositions. The participants’ task was to indicate which of the first two premises they believed more after receiving the fact. We found that the belief in the conditional premise dropped significantly when this premise was stated by a low- rather than a high- trustworthy source. Moreover we found that the conditional premise was believed more in MT than in MP problems. Both findings are best explained by the conditional probability hypothesis (e.g., Evans et al., 2003)”

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