A Context-Specific Measure of Psychological Inflexibility in Therapist Training: Development of the KIBS-Ed

AbstractObjectives. Psychological inflexibility (PI) is a potentially important yet understudied factor in therapist training. However, validated instruments tailored to trainee contexts are currently lacking. This study aimed to develop and evaluate a new measure of PI in psychotherapy education settings. Results. In Study One, an initial version of the scale was developed and tested with 195 mental health professionals. Preliminary psychometric evaluation included expert review, cognitive interviews, exploratory factor analysis, and Mokken scale analysis. Rasch methodology was then applied to assess dimensionality, item independence, response category ordering, targeting, invariance, and reliability. In Study Two, a new sample (n = 337) was used to validate the revised instrument through Rasch analysis. Results supported a unidimensional, 7-item scale demonstrating good model fit, local independence, ordered thresholds, invariance, and acceptable reliability. Additional analyses suggested a small but statistically significant negative association between age and psychological inflexibility (rho = -0.18), while no consistent differences were found across gender or profession. Conclusion. The resulting instrument – the Karolinska Inner-Barriers Scale for Education (KIBS-Ed) – offers a psychometrically sound, context-specific tool for assessing psychological inflexibility in psychotherapy training. It supports empirical investigations of trainee processes and may inform future research on therapist development and education.