The use of the Symptom Checklist 90-R in exploring the factor structure of mental disorders and the neglected fact of comorbidity.

The Symptom Checklist 90-R (SCL-90-R) is a popular instrument, accessing nine different symptom clusters of psychopathology, although its original factor structure is widely questioned. However, most validation studies seem to ignore the possible effect of comorbidity. We aimed at validating the factor structure of the SCL-90-R and to draw additional information about the role of comorbidity in the factor structure of mental disorders. We thus introduced a comorbidity index within the SCL-90-R and validated the Greek version of the SCL-90-R in a sample of 914 participants, consisting of 688 individuals from the general population and 226 psychiatric outpatients. We showed that the original 9-factor model was superior to the second order factor and the bi-factor model. This may reflect lower comorbidity traits in our sample, rather than the accuracy of the original 9-factor structure of the SCL-90-R, which has to be further assessed by concurrent validity for each individual scale on selected samples. In this regard, we showed that the depression subscale was an excellent screening tool in a subgroup of patients with a confirmed major depressive episode.