This page contains all the collected study materials and instructions from authors that we have compiled. We also include any comments from other contributors or follow up instructions that we have learned since the beginning of the project. Click "read more" below or choose the "Wiki" option above for further information. For technical problems, please contact OSF help desk (firstname.lastname@example.org) For questions or information about the studies contact either either Jon Grahe (email@example.com) or Mark Brandt (firstname.lastname@example.org) so that the materials can be made available on this website.
Major recent interpretations of the conjunction fallacy postulate that people assess the probability of a conjunction according to (non-normative) averaging rules as applied to the constituents' probabilities or represent the conjunction fallacy as an effect of random error in the judgment process. In the present contribution, we contrast such accounts with a different reading of the phenomenon based on the notion of inductive confirmation as defined by contemporary Bayesian theorists. Averaging rule hypotheses along with the random error model and many other existing proposals are shown to all imply that conjunction fallacy rates would rise as the perceived probability of the added conjunct does. By contrast, our account predicts that the conjunction fallacy depends on the added conjunct being perceived as inductively confirmed. Four studies are reported in which the judged probability versus confirmation of the added conjunct have been systematically manipulated and dissociated. The results consistently favor a confirmation–theoretic account of the conjunction fallacy against competing views. Our proposal is also discussed in connection with related issues in the study of human inductive reasoning.
The original paper is [here] (will require a library subscription).
The materials for Experiment 3 are in Appendix C of the paper. We also have the materials for Experiment 4 (this is *not* the CREP replication) in the files section that can be used to create similarly designed materials. They are in Italian, but should give a good rough guide to how the experiment was presented.
**Suggestions/Hints/Instructions from Original Author**
Please keep also in mind that:
Confirmation judgments do not have to be confused with probability judgments, and the experimenter(s) should have VERY clear in their minds the distinction between the two before collecting data (so to avoid making mistakes when they explain the tasks to participants).