ASSESSMENT Relevance of the Thought–Shape Fusion Trait Questionnaire for healthy women and women presenting symptoms of eating disorders and mixed mental disorders Andrea Wyssen 1 | Luka J. Debbeler 2 | Andrea H. Meyer 3 | Jennifer S. Coelho 4,5 | Nadine Humbel 1 | Kathrin Schuck 6 | Julia Lennertz 6 | Nadine Messerli‐Bürgy 1 | Stephan N. Trier 7 | Bettina Isenschmid 8 | Gabriella Milos 9 | Hanspeter Flury 10 | Silvia Schneider 6 | Simone Munsch 1 1 Department of Psychology, Clinical Psychology and Psychotherapy, University of Fribourg, Fribourg, Switzerland 2 Department of Psychology, Psychological Assessment and Health Psychology, University of Konstanz, Constance, Germany 3 Institute of Psychology, Clinical Psychology and Epidemiology, University of Basel, Basel, Switzerland 4 Provincial Specialized Eating Disorders Program for Children and Adolescents, British Columbia Children's Hospital, Vancouver, Canada & Department of Psychiatry, University of British Columbia, Vancouver, Canada 5 Department of Psychiatry, University of British Columbia, Vancouver, Canada 6 Faculty of Psychology, Mental Health Research and Treatment Center, Ruhr‐ University Bochum, Bochum, Germany 7 Privatklinik Aadorf, Aadorf, Switzerland 8 Kompetenzzentrum für Essverhalten, Adipositas und Psyche Spital Zofingen, Zofingen, Switzerland 9 Klinik für Konsiliarpsychiatrie und Psychosomatik, Medizinische Fakultät, Universitätsspital Zürich, Zürich, Switzerland 10 Privatklinik Schützen, Rheinfelden, Switzerland Correspondence Simone Munsch, PhD, Department für Psychologie, Klinische Psychologie und Psychotherapie, Universität Fribourg, 2, Rue de Faucigny, CH‐1700 Fribourg, Switzerland. Email: simone.munsch@unifr.ch Funding information Swiss National Science Foundation, Grant/ Award Number: 100014L_149416/1; German Research Foundation, Grant/Award Number: SCHN 415/4‐1; Swiss Anorexia Nervosa Foundation, Grant/Award Number: 22‐12; Research Fund of the University of Fribourg, Grant/Award Number: 419 Thought–shape fusion (TSF) describes the experience of marked concerns about body weight/ shape, feelings of fatness, the perception of weight gain, and the impression of moral wrongdoing after thinking about eating fattening/forbidden foods. This study sets out to evaluate the short version of the TSF trait questionnaire (TSF). The sample consists of 315 healthy control women, 244 women with clinical and subthresh- old eating disorders, and 113 women with mixed mental disorders (mixed). The factor structure of the TSF questionnaire was examined using exploratory and subsequent confirma- tory factor analyses. The questionnaire distinguishes between a Concept scale and a Clinical Impact scale. However, a lack of measurement invariances refers to significant differences between groups in terms of factor loadings, thresholds, and residuals, which questions cross‐group validity. Results indicate that the concept is understood differently in the 3 groups and refers to the suitability of the questionnaire primarily for individuals presenting with symptoms of eating disorders. KEYWORDS cognitive distortions, confirmatory factor analysis, eating disorders, thought–shape fusion, women Received: 27 October 2017 Revised: 25 January 2018 Accepted: 26 January 2018 DOI: 10.1002/cpp.2186 Clin Psychol Psychother. 2018;1–7. Copyright © 2018 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/cpp 1