Evaluation of the psychometric properties of the Icelandic version of the CORE- OM, its transdiagnostic utility and cross cultural validation Short title: Psychometric properties and transdiagnostic utility of the Icelandic CORE-OM

Background: Development of transdiagnostic standardised measures of psychological distress have contributed to the development of practice based evidence networks. The translation and validation of such measures cross culturally is important if such research is to be generalised across health care systems in different countries. Method: Translation of the Clinical Outcomes in Routine Evaluation Outcome Measure (CORE-OM) from English into Icelandic was undertaken according to recommended protocols. The resulting instrument was evaluated for reliability and validity in three groups; patients undergoing psychological treatment in general practice (n= 289), psychiatric outpatients (n=98) and student controls (n=207). Clinical participants underwent diagnostic interview were the MINI-International Neuropsychiatric Interview were administered. The clinical participant also completed the CORE-OM and the Beck Depression and Anxiety Inventories before and after treatment. The transdiagnostic relationship between CORE-OM scores and scores on those diagnostic measures was assessed. Results: Good levels of validity, reliability and internal consistency were found for the CORE-OM and its domains and sensitivity to change over treatment shown. As anticipated, the Risk domain had different characteristics than other domains. COREOM scores correlated strongly with both BDI-II and BAI, particularly the problem domain. Conclusion: The Icelandic translation of the CORE-OM is psychometrically sound and can be applied in Icelandic mental health studies as it has been in English speaking settings. Nevertheless the validity of the Icelandic version of the CORE-OM needs to further investigate in larger and more diverse samples