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

BackgroundThe factor structure and dimensionality of the HAM-D17 and the IDS-C30 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).MethodsThe first treatment step (Level 1) in the STAR*D study provided a dataset of 4041 outpatients with DSM-IV nonpsychotic major depression. The HAM-D17 and IDS-C30 were evaluated by principal component analysis (PCA) without rotation. Mokken analysis tested the unidimensionality of the IDS-C6, which corresponds to the unidimensional HAM-D6.ResultsFor both the HAM-D17 and IDS-C30, PCA identified a bi-directional factor contrasting the depressive symptoms versus the neurovegetative symptoms. The HAM-D6 and the corresponding IDS-C6 symptoms all emerged in the depression factor. Both the HAM-D6 and IDS-C6 were found to be unidimensional scales, i.e., their total scores are each a sufficient statistic for the measurement of depressive states.LimitationsSTAR*D used only one medication in Level 1.ConclusionsThe unidimensional HAM-D6 and IDS-C6 should be used when evaluating the pure clinical effect of antidepressive treatment, whereas the multidimensional HAM-D17 and IDS-C30 should be considered when selecting antidepressant treatment.