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Original Research ARTICLE

Front. Psychol. | doi: 10.3389/fpsyg.2020.560273

When success is not enough: The symptom base-rate can influence judgments of effectiveness of a successful treatment Provisionally accepted The final, formatted version of the article will be published soon. Notify me

  • 1University of Deusto, Spain

Patients' beliefs about the effectiveness of their treatments are key to the success of any intervention. However, since these beliefs are usually formed by sequentially accumulating evidence in the form of the covariation between the treatment use and the symptoms, it is not always easy to detect when a treatment is actually working. In Experiments 1 and 2, we presented participants with a contingency learning task in which a fictitious treatment was actually effective to reduce the symptoms of fictitious patients. However, the base-rate of the symptoms was manipulated so that, for half of participants, the symptoms were very frequent before the treatment, whereas for the rest of participants, the symptoms were less frequently observed. Although the treatment was equally effective in all cases according to the objective contingency between the treatment and healings, the participants' beliefs on the effectiveness of the treatment were influenced by the base-rate of the symptoms, so that those who observed frequent symptoms before the treatment tended to produce lower judgments of effectiveness. Experiment 3 showed that participants were probably basing their judgments on an estimate of effectiveness relative to the symptom base-rate, rather than on contingency in absolute terms. Data and materials are publicly available at the Open Science Framework:

Keywords: causal learning, cognitive bias, Patients' beliefs, Base-rates, causal judgment

Received: 08 May 2020; Accepted: 26 Aug 2020.

Copyright: © 2020 Blanco, Moreno-Fernández and Matute. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Fernando Blanco, University of Deusto, Bilbao, Spain,