Factor structure and dimensionality of the two depression scales in STAR*D using level 1 datasets

Background: The factor structure and dimensionality of the HAM-D-17 and the IDS-C-30 are as yet uncertain, because psychometric analyses of these scales have been performed without a clear separation between factor structure profile and dimensionality (total scores being a sufficient statistic). Methods: The first treatment step (Level 1) in the STAR*D study provided a dataset of 4041 outpatients with DSM-IV nonpsychotic major depression. The HAM-D-17 and IDS-C-30 were evaluated by principal component analysis (PCA) without rotation. Mokken analysis tested the unidimensionality of the IDS-C-6, which corresponds to the unidimensional HAM-D-6. Results: For both the HAM-D-17 and IDS-C-30, PCA identified a bi-directional factor contrasting the depressive symptoms versus the neurovegetative symptoms. The HAM-D-6 and the corresponding IDS-C-6 symptoms all emerged in the depression factor. Both the HAM-D-6 and IDS-C-6 were found to be unidimensional scales, i.e., their total scores are each a sufficient statistic for the measurement of depressive states. Limitations: STAR*D used only one medication in Level 1. Conclusions: The unidimensional HAM-D-6 and IDS-C-6 should be used when evaluating the pure clinical effect of antidepressive treatment, whereas the multidimensional HAM-D-17 and IDS-C-30 should be considered when selecting antidepressant treatment. (C) 2011 Elsevier B.V. All rights reserved.