Psychometric properties of the action and acceptance questionnaire for trichotillomania in a clinical sample of patients with trichotillomania and skin picking disorder

Self-report questionnaires can be valuable for evaluating treatment processes and outcomes in Acceptance and Commitment Therapy enhanced Behavioral Therapy (ACT-enhanced BT) for trichotillomania (TTM) and skin picking disorder (SPD). The Action and Acceptance Questionnaire for TTM (AAQ-4TTM) assesses experiential avoidance in individuals with TTM and can be easily adapted for patients with SPD by replacing references to “hair pulling” with “skin picking.” This study aims to evaluate the psychometric properties of the AAQ-4TTM, including factor structure, factor loadings, internal consistency, and construct validity, in a treatment-seeking sample of individuals with TTM or SPD. We expected no differences in factor structure and other psychometric properties across the two diagnostic groups. The study sample comprised 244 patients with a primary diagnosis of TTM (n = 144) or SPD (n = 100), all of whom were evaluated for ACT-enhanced BT. Contrary to our prediction, the exploratory factor analyses revealed different factor structures for the SPD group compared to the TTM group. While a two-factor structure emerged in the TTM group, a unidimensional structure was found in the SPD group. In TTM, the two factors were labeled “Acceptance” and “Interference”. The Interference factor showed stronger associations with measures of psychopathology than the Acceptance factor. The SPD factor, labeled “Flexibility”, showed the strongest correlation with self-reported skin-picking severity. Although the psychometric properties of the AAQ-4TTM were not optimal, the two factors identified in the TTM group seem to represent meaningful constructs within the ACT framework. In the SPD group, the AAQ-4SPD appears to function as a unidimensional scale, reflecting Psychological flexibility.