Validation of the Danish Version of the Overall Depression Severity and Impairment Scale (ODSIS): A Reliable Instrument for Assessing Depression Symptoms and Functional Impairment.

Introduction: In psychotherapy, having a reliable tracking tool is vital for effective treatment. We have validated the Danish version of the 'Overall Depression Severity and Impairment Scale' (ODSIS), which is used in the Unified Protocol for Emotional Disorders (UP) and other cognitive behavioural therapies. This five-item self-rating scale is expected to correspond closely to the gold-standard Beck Depression Inventory-II (BDI-II), but also to self-rating scales addressing daily functioning and well-being.

Methods: Internal consistency is assessed using Cronbach's alpha and McDonald's omega. Criterion validity is explored through Pearson's correlation coefficient with BDI-II, the Work and Social Adjustment Scale (WSAS), the Five-Item World Health Organization Well-Being Index (WHO-5) and scatter plots, and an optimal cut-off score is determined using a receiver operating characteristic curve. The study included 340 respondents: 234 from a recent clinical trial, 56 psychiatric patients from inpatient/outpatient units and 50 healthy volunteers.

Results: ODSIS demonstrates strong internal consistency (Cronbach's alpha: 0.887-0.956, McDonald's omega: 0.888-0.957). Correlations with BDI-II, WSAS and WHO-5 highlight its strong criterion validity (BDI-II: 0.847, WSAS: 0.751, WHO-5: 0.771). The optimal cut-off score (> 7.5) for detecting depression shows great sensitivity (0.862) and specificity (0.731).

Conclusion: The Danish version of ODSIS proves to be a reliable instrument for quantification of a combination of depression level and functional impairment from the symptoms. Its high correlation with established BDI-II makes it a brief and handy tool for repeated measurement in clinical and research settings.