Does Change over Time in Delusional Beliefs as Measured with PDI Predict Change over Time in Belief Flexibility Measured with MADS?


Delusional beliefs and their behavioral consequences are predominant symptoms in patients with psychosis and play an important role in the treatment. Delusional beliefs are a multidimensional concept which can be divided into three components: distress, preoccupation and conviction of delusions. These can be measured using Peters delusions inventory (PDI-21). We question, whether changes in delusional beliefs over time during treatment measured with the PDI-21 can predict changes in belief flexibility measured with the Maudsley assessment of delusions schedule (MADS). We used a group of patients from a randomized controlled trial for a cognitive intervention for psychosis or psychotic symptoms. Aside standard treatment for psychosis, half of the patients took part in a group treatment “Michael’s game”. Patients were assessed at baseline (T1), at 3 months (T2), and at 9 months (T3). We measured delusional beliefs using PDI-21 and belief flexibility with the MADS. One hundred seventy-two patients were included in the analysis. We measured a main effect of PDI-21scores on belief flexibility measured with MADS. PDI-21 Conviction scores predicted outcomes for all measured MADS items. Increasing PDI Distress and Preoccupation scores were predictors for being more likely to dismiss beliefs and change conviction. Time itself was a predictor for changing conviction and being able to plan a behavioral experiment. Overall the changes in PDI scores predicted outcomes for belief flexibility measured with MADS items. The PDI-21 could be a simple and effective way to measure progress in treatment on delusional beliefs.

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We thank the participants and the game leaders, as well as Karen Dieben, Gregoire Monney, Virginie Salamin, Dr. Fethi Bretel, Silke Azoulay, Elodie Pesenti, Raoul Krychowski, Andreia Costa Prata, Dr. Alexei Traian, Dr. Thomas Charpeaud, Prof. Daniele Zullino, Prof. Alberto Parabiaghi, Joanne Corpataux, Milena Kriz, Dr. Giacomini, Claude Hayoz (Fondation HorizonSud), Dr. Georges Klein, Phillippe Laffond, Prof. Eric Bonvin, Prof. Sonia Dollfus, Prof. Thierry D’Amato, Prof. Jean-Michel Llorca, Dr. George Berthon, Dr. Céline Plassereaud, Dr. Véronique Roure, Natacha Boureykoff, Marie-Josée Durak, Dr. Maria Teresa Caldera, Dr. Roberta Bossoletti, and Dario Caffaro. Funding: Swiss National Science Foundation Grant 32003B-121038.

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All authors contributed to the study conception and design of the original study. Louise Penzenstadler and Yasser Khazaal contributed to the conception and design of the secondary analysis. The formal analysis was performed by Anne Chatton. The first draft of the manuscript was written by Louise Penzenstadler, Jérôme Favrod and Yasser Khazaal and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Louise Penzenstadler.

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Disclosure of Potential Conflicts of Interest

This study was funded by Swiss National Science Foundation Grant 32003B-121038. Yasser Khazaal and Jérôme Favrod are the authors of the game. The other co-authors declare that the research was conducted in the absence of any commercial or financial relationships that could be conceived as a potential conflict of interest.

Research Involving Human Participants and/or Animals

All procedures performed in studies involving human participants were in accordance with the ethical standards of the national research committees. The ethical committees of all four countries approved the trial. The protocol was registered (International Standard Randomized Controlled Trial Number Register: ISRCTN37178153) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.”

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Informed consent was obtained from all individual participants included in the study.

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Penzenstadler, L., Chatton, A., Huguelet, P. et al. Does Change over Time in Delusional Beliefs as Measured with PDI Predict Change over Time in Belief Flexibility Measured with MADS?. Psychiatr Q 90, 693–702 (2019).

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  • Psychosis
  • Schizophrenia
  • Delusional beliefs
  • Belief flexibility
  • Cognitive behavior therapy