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-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).

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-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-D_6.

Results

For 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.

Limitations

STAR*D used only one medication in Level 1.

Conclusions

The 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.