Item response theory analysis of Centers for Disease Control and Prevention Health-Related Quality of Life (CDC HRQOL) items in adults with arthritis

Table 2 Parameter estimates from the GRM for the CDC-Physical and Mental Health

Item description	a	b₁	b₂	b₃	b₄	b₅	b₆	b₇
CDC-physical health
HDCM 1:	2.24	−2.35	−1.05	0.12	1.51	-	-	-
General health	2.24	−2.35	−1.05	0.12	1.51	-	-	-
HDCM 2:	3.52	−0.98	−0.44	−0.06	0.24	0.52	0.86	1.04
Physical health not good	3.52	−0.98	−0.44	−0.06	0.24	0.52	0.86	1.04
HDCM 4:	2.77	−0.27	0.08	0.38	0.66	0.92	1.24	1.49
Poor health	2.77	−0.27	0.08	0.38	0.66	0.92	1.24	1.49
HDSM 1:	2.97	−0.74	−0.27	0.01	0.26	0.47	0.75	0.94
Pain limited activities	2.97	−0.74	−0.27	0.01	0.26	0.47	0.75	0.94
HDSM 5:	1.73	−2.2	−1.34	−0.97	−0.61	−0.27	0.10	0.47
Full of energy^a	1.73	−2.2	−1.34	−0.97	−0.61	−0.27	0.10	0.47
CDC-Mental Health
HDCM 3:	4.10	−0.47	0.01	0.34	0.64	0.89	1.18	1.4
Mental health not good	4.10	−0.47	0.01	0.34	0.64	0.89	1.18	1.4
HDSM 2:	7.71	−0.44	0.05	0.38	0.67	0.89	1.13	1.32
Sad, blue, depressed	7.71	−0.44	0.05	0.38	0.67	0.89	1.13	1.32
HDSM 3:	3.45	−0.71	−0.11	0.25	0.54	0.78	1.03	1.19
Worried, tense, anxious	3.45	−0.71	−0.11	0.25	0.54	0.78	1.03	1.19

GRM graded response model, HDCM 4-item Healthy Days Core Module (# days except for HDCM 1), HDSM4 5-item Healthy Days Symptoms Module omitting the rest item (# days)
^aHDSM 5 Full of energy was reversed scored for all analyses

ISSN: 1477-7525