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The Zero-Sum Fallacy in Evidence Evaluation

Pilditch, TD; Fenton, N; Lagnado, D; (2019) The Zero-Sum Fallacy in Evidence Evaluation. Psychological Science , 30 (2) pp. 250-260. 10.1177/0956797618818484. Green open access

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Abstract

There are many instances, both in professional domains such as law, forensics, and medicine and in everyday life, in which an effect (e.g., a piece of evidence or event) has multiple possible causes. In three experiments, we demonstrated that individuals erroneously assume that evidence that is equally predicted by two competing hypotheses offers no support for either hypothesis. However, this assumption holds only in cases in which competing causes are mutually exclusive and exhaustive (i.e., exactly one cause is true). We argue that this reasoning error is due to a zero-sum perspective on evidence, wherein people assume that evidence that supports one causal hypothesis must disconfirm its competitor. Thus, evidence cannot give positive support to both competitors. Across three experiments (N = 49, N = 193, N = 201), we demonstrated that this error is robust to intervention and generalizes across several different contexts. We also ruled out several alternative explanations of the bias.

Type: Article
Title: The Zero-Sum Fallacy in Evidence Evaluation
Open access status: An open access version is available from UCL Discovery
DOI: 10.1177/0956797618818484
Publisher version: https://doi.org/10.1177/0956797618818484
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: zero sum, intuitive judgment, cognitive bias, evidential reasoning, probabilistic reasoning, open data, open materials
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > Div of Psychology and Lang Sciences
UCL > Provost and Vice Provost Offices > School of Life and Medical Sciences > Faculty of Brain Sciences > Div of Psychology and Lang Sciences > Experimental Psychology
URI: https://discovery.ucl.ac.uk/id/eprint/10068067
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