[Broad scope symptom questionnaires in psychotherapy: Comparing Brief Symptom Inventory and ICD-10 Symptom Rating]

Our study compared the psychometric properties of two broad scope symptom questionnaires, the Brief Symptom Inventory [7] and the ICD-10 Symptom Rating Scale [8], in a naturalistic data set of 507 patients in outpatient psychotherapeutic treatment. Reliability of total scores and subscale scores were estimated via internal consistency coefficients Cronbach's α and McDonald's ω. Measurement precision was operationalized via the uncertainty interval. Validity of the total scores as measures of symptom load was operationalized via convergence analysis with measures similar and dissimilar to that concept. Validity of the internal structure of each scale was operationalized via confirmatory factor analysis of multiple models established in literature. Reliability and measurement precision were comparable for the two questionnaires. The convergent and discriminant validity of both instruments appear to be similarly sufficient. The ISR clearly showed good factorial validity, whereas the BSI was found to have poor factorial validity. Due to its uncertain factorial structure, interpretation of the BSI subscales is not advised. In sum, the ISR and BSI have comparable reliability and measurement precision, but ISR has superior validity and better time efficiency and therefore can be considered a valid alternative to the BSI.