Table 3. Analysis of psychometric validity/unidimensionality of the 17-item Hamilton depression rating scale (HAM-D₁₇) and the 6-item melancholia subscale (HAM-D₆).

	Loevinger coefficients of homogeneity
	STOP-PD (n=210)	STAR*D [45] (n=2323)	Licht et al. 2005 [44] (n=1459)
HAM-D17	0.30	0.32	0.28
HAM-D6	0.50	0.48	0.49

Mokken analysis of the HAM-D₁₇ and the HAM-D₆ scores at week 4 across three studies: the Study of Pharmacotherapy of Psychotic Depression (STOP-PD), the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) and “Validation of the Bech-Rafaelsen Melancholia Scale and the Hamilton Depression Scale in patients with major depression; is the total score a valid measure of illness severity?” (Licht et al 2005). The results are expressed as Loevinger coefficients of homogeneity, where values ≥ 0.40 indicate unidimensionality.