Table 2.

Item response theory (IRT) parameter estimates for the 23 domain versions of the IDS (IDS-C28 and the IDS-SR28)

Domain	IDS-C30				IDS-SR30				Diff.
	a	b0	b1	b2	a	b0	b1	b2
1. Sleep	1.17	−2.62	−1.48	0.00	1.17	−2.62	−1.48	0.00
2. Sad mood	2.85	−0.98	0.11	1.03	2.85	−0.98	0.11	1.03
3. Irritability	1.59	−0.77	0.58	1.83	1.59	−0.77	0.58	1.83
4. Anxiety/Tension	1.85	−1.20	0.00	1.18	1.85	−1.20	0.00	1.18
5. Response to events	1.99	0.10	0.73	1.43	1.99	0.10	0.56	1.43	b2
6. Diurnal variation	0.55	0.78			0.55	0.78
7. Distinct quality to mood	0.55	−0.52			1.65	−0.52			a
8. Appetite/Weight	0.74	−1.24			0.74	−1.24
9. Concentration/Decision making	1.58	−0.57	0.38	1.40	1.96	−0.57	0.38	1.40	a
10. Self view	2.07	0.02	0.72	1.29	2.07	0.02	0.72	1.09	b3
11. Future view	1.97	−0.28	0.58	1.36	1.97	−0.54	0.58	1.36	b1
12. Thoughts of death/Suicide	1.80	0.53	1.69	2.90	1.80	0.53	1.69	2.90
13. General interest	2.23	−0.24	0.50	1.22	2.23	−0.24	0.50	1.22
14. Energy level	1.95	−0.52	0.32	1.24	1.95	−0.52	0.32	1.24
15. Capacity for pleasure	1.98	0.18	0.70	1.25	2.71	−0.13	0.70	1.43	a, b3
16. Interest in sex	1.12	−0.36			1.12	−0.36
17. Restlessness/Agitation	1.54	−0.94	0.67	3.30	1.10	−0.94	0.67	1.84	a,–b3
18. Aches and pains	0.92	−1.89	0.01	1.26	0.92	−1.89	0.01	1.26
19. Sympathetic arousal	1.17	−1.01	0.81	2.05	1.17	−1.01	0.81	2.05
20. Panic/Phobia	1.23	0.27	0.88	2.25	1.23	−0.07	1.16	1.78	b1,b2,b3
21. Gastrointestinal complaints	0.66	0.59			0.66	0.59
22. Interpersonal sensitivity	1.34	0.07	0.61	1.66	1.34	−0.30	0.90	1.66	b1,b2
23. Physical energy	1.42	0.06	0.89	1.70	1.42	0.06	0.89	1.70

Notes: Diff = parameter estimates that differ between the clinical and self-report versions, ie, exhibit dif.