Objective: Evaluation of antidepressant drug efficacy requires adequate rating scales for measuring the severity of depression. However, to measure the illness severity by such a total score, the scale needs to fulfil criteria of unidimensionality. On this background, we aimed at comparing the unidimensionality of the Bech–Rafaelsen Melancholia Scale (MES) and the 17-item Hamilton Depression Rating Scale (HAM-D17).
Method: A total of 1629 patients aged between 18 and 65 years with a major depressive episode were treated openly with sertraline at a fixed oral dose of 50 mg daily during 4 weeks. The HAM-D17 and the MES were applied at baseline and at weeks 2 and 4. Unidimensionality was tested with Mokken and Rasch analysis.
Results: Unidimensionality of the HAM-D17 could not be confirmed. However, the 6-item Hamilton Depression Subscale (HAM-D6), was accepted by the Rasch analysis both at baseline and after 2 and 4 weeks of therapy. For the MES (as well as for the HAM-D6), a Loevinger coefficient of homogeneity above 0.40 (suggesting acceptance) was found at week 4.
Conclusion: The HAM-D6 and the MES did fulfil criteria for unidimensionality while the HAM-D17 did not. Therefore, the extended use of the HAM-D17 in drug trials may be questioned.