The SCL-90 and SCL-90R versions validated by item response models in a Danish community sample

Objective: To evaluate the internal validity of the subscales of the combined SCL-90 and SCL-90R, the SCL-92, by item response analyses as compared with several previously reported factor analyses of this questionnaire in the literature. Method: The SCL-92 questionnaire was mailed to an age- and gender-stratified random sample of Danish citizens. The sample comprised 2040 individuals. The internal structure of the nine factors of the SCL-92 questionnaire was evaluated by Mokken-Loevinger analysis and Rasch analysis. Results: In total, 1153 persons or 58% returned the questionnaire fully completed. Mokken analysis found all scales apart from the psychoticism scale acceptable. The Rasch analysis found most of the subscales to be robust. Minor problems were seen for the scales of phobic anxiety, obsession-compulsion and depression. Analysis of the Global Severity Index showed that the Rasch model was rejected for the full 92-item scale, but not for a scale consisting of the 63 items from the non-psychotic subscales. Spearman correlations among the subscales were all positive (range 0.34-0.79) and so were correlations between each of the subscales and the Global Severity Index (range 0.55-0.91). Conclusion: In this sample from the Danish general population the non-psychotic subscales, i.e. the subscales covering psychological distress were observed to function well. In a general population sample, the 63 non-psychotic items primarily appear to reflect one broad dimension of distress.