Supplementary materials [Test] to: Development and initial validation of a brief questionnaire on the patients’ view of the in-session realization of the six core components of Acceptance and Commitment Therapy

Background: Assessing in-session processes is important in psychotherapy research. The aim of the present study was to create and evaluate a short questionnaire capturing the patients’ view of the in-session realization of the six core components of Acceptance and Commitment Therapy (ACT). Method: In two studies, psychotherapy patients receiving ACT (Study 1: n = 87) or Cognitive-Behavioral Therapy (CBT) (Study 2, Sample 1: n = 115; Sample 2: n = 156) completed the ACT session questionnaire (ACT-SQ). Therapists were n = 9 ACT therapists (Study 1) and n = 77 CBT trainee therapists (Study 2). Results: Factor structure: Exploratory factor analyses suggested a one-factor solution for the ACT-SQ. Reliability: Cronbach’s alpha of the ACT-SQ was good (Study 1: α = .81; Study 2, Sample 1: α = .84; Sample 2: α = .88). Convergent validity: The ACT-SQ was positively correlated with validated psychotherapeutic change mechanisms (p < .05). Criterion validity: Higher ACT-SQ scores were associated with better treatment outcomes (p < .05). Conclusion: The study provides preliminary evidence for the reliability and validity of the ACT-SQ to assess the in-session realization of the six core components of ACT in the patients’ view. Further validation studies and ACT-SQ versions for therapists and observers are necessary.