Table 2.

Results from IRT analysis, item discrimination, and item difficulty parameters

EQ-5D	(a) Item discrimination	(b) Item difficulty
Pain/discomfort	1.75
≥ 2		− 0.42
= 3		0.90
Mobility	1.74
≥ 2		0.92
= 3		4.52
Self-care	1.56
≥ 2		2.66
= 3		4.58
Anxiety/depression	0.84
≥ 2		− 1.37
= 3		1.18
Usual activities	0.67
≥ 2		0.45
= 3		4.03

SF-6D	(a) Item discrimination	(b) Item difficulty
Mental health	1.97
≥ 2		− 1.48
≥ 3		− 0.37
≥ 4		0.95
= 5		1.69
Role limitation	1.90
≥ 2		− 0.82
≥ 3		− 0.46
= 4		0.58
Social functioning	1.73
≥ 2		− 0.63
≥ 3		− 0.20
≥ 4		0.51
= 5		1.19
Vitality	1.53
≥ 2		− 2.07
≥ 3		− 1.04
≥ 4		0.22
= 5		1.55
Pain	1.03
≥ 2		− 0.60
≥ 3		0.15
≥ 4		1.09
= 5		2.24
Physical functioning	1.03
≥ 2		0.86
= 3		2.34