Tendency for people to evaluate deductive arguments based on the believability of the conclusion rather than its logical validity.
Evans, J. S. B., Barston, J. L., & Pollard, P. (1983). On the conflict between logic and belief in syllogistic reasoning. Memory & Cognition, 11(3), 295–306.
Participants are instructed to evaluate syllogisms by indicating whether the conclusion necessarily follows from the premises or not, assuming that all premises are true. The rationale is to assess the effect of the believability of the conclusion (believable vs. unbelievable) for a given level of validity of the argument (valid vs. invalid). Eight pairs of syllogisms are used, each pair involving a consistent item and an inconsistent one. On eight inconsistent items, the logical validity of the argument is incongruent with the believability of the conclusion (two of them are valid but unbelievable, and two are invalid but believable). On eight consistent items, the logical validity of the argument is congruent with the believability of the conclusion (two of them are both valid and believable, and two are both invalid and unbelievable).
The total score is the number of biased responses. A response is coded as biased if the participant provided an incorrect answer to an inconsistent item and a correct answer to the corresponding consistent item.
Teovanović, P., Knežević, G., & Stankov, L. (2015). Individual differences in cognitive biases: Evidence against one-factor theory of rationality. Intelligence, 50, 75–86.
See also: Berthet V. (2021). The Measurement of Individual Differences in Cognitive Biases: A Review and Improvement. Frontiers in psychology, 12, 630177.