Intersession Experience Questionnaire Short (IEQ-S): psychometric properties and longitudinal associations with...

Intersession experiences - thoughts, feelings, and fantasies about therapy or the therapist between sessions - are relevant markers of therapeutic engagement and internalization. However, existing measures like the Intersession Experience Questionnaire (IEQ) are lengthy and difficult to implement in routine care. This study aimed to develop and evaluate a brief, psychometrically sound version of the IEQ that retained the most important dimensions, the Intersession Experience Questionnaire-Short (IEQ-S), to facilitate repeated assessments in clinical and research settings.Based on the German IEQ, eight items with the highest factor loadings across conceptual domains were selected. Cross-sectional data from five clinical samples (N=165) and longitudinal data from another sample of 72 outpatients (2,119 sessions) were used to examine the factor structure, reliability, and validity of the IEQ-S, as well as its sensitivity to within-person change.The IEQ-S items demonstrated strong convergence with the single factors of the full IEQ. It showed expected associations with therapeutic alliance and symptom burden, while demonstrating discriminant validity against general health. Longitudinal analyses revealed meaningful within-person variability and statistically significant associations with depressive symptoms over time (i. e., session by session).The IEQ-S is a reliable, valid, and efficient instrument for capturing intersession experiences. Conclusion: The IEQ-S's brevity and dynamic sensitivity make it well-suited for routine monitoring and ecological momentary assessment. Further research should explore its prognostic utility and applicability across therapy formats.