Comparison of commonly applied outcome inventories as measures of general internalizing pathology in psychological therapies

Measuring general factors to capture severity of psychopathology broadly can be useful for assessing treatment outcomes of psychological therapies. Namely, general factors are suitable for broadband measurement, which has become increasingly important due to efforts to standardize outcome measurement. Reasons for measuring general factors include their predictive validity, relatability to parallel research in epidemiology, genetics and neurobiology, simplicity due to unidimensionality, longitudinal structural validity and potential for capturing transdiagnostic change. Psychotherapy register data (N = 5223; 4059, 77.7%, identify as female) of Finnish speaking adult patients entering psychological therapy were used to compare three patient self-report inventories suggested for routine use—Patient Health Questionnaire-9 (PHQ-9), Clinical Outcomes in Routine Evaluation–Outcome Measure (CORE-OM) and CORE-10—as measures of a general internalizing pathology factor. A multidimensional factor model was estimated, and noise factors were marginalized out of the analysis. Fisher information about internalizing was computed for each inventory. CORE-OM had high total Fisher information about internalizing, but per item information was markedly lower compared to CORE-10. Surprisingly, though not included a priori in the set of compared inventories, the Overall Anxiety Severity and Impairment Scale (OASIS) was as effective as CORE-10 per item, though OASIS provided low total information due to only comprising five items and was confounded by an anxiety specific factor. PHQ-9 did not perform well as a measure of internalizing. Results suggested CORE-10 to be a valid, brief, option for broadband outcome measurement in psychological therapies.